Biomedical subjects

R A DeFronzo

Publications and source records attributed to R A DeFronzo.

At least 55 records · Page 3Linked to original sources

PubMed1997

Insulin resistance: a multifaceted syndrome responsible for NIDDM, obesity, hypertension, dyslipidaemia and atherosclerosis.

Insulin resistance syndrome (IRS) has the potential to explain a large group of common metabolic and cardiovascular disorders [e.g., obesity, non-insulin-dependent diabetes mellitus (NIDDM), hypertension, hyperlipidaemia, hypercoagulability] which are all in themselves cardiovascular risk factors. This contribution firstly reviews the convincing evidence from glucose-clamp studies that all of these conditions are characterised by the presence of combined insulin resistance and hyperinsulinaemia, and secondly examines the relationships of the components of this syndrome to coronary artery disease and to the rational choice of antihypertensive therapy.

Arteriosclerosis↗

PubMed1997

Chronic hyperinsulinemia inhibits platelet-activating factor (PAF) biosynthesis in the rat kidney.

A number of risk factors for cardiovascular disease, including hypertension, are associated with the insulin resistance syndrome. The hallmark of this syndrome is an impairment in insulin action which provokes a compensatory increase in pancreatic beta-cell insulin secretion leading to chronic hyperinsulinemia. Indirect studies show that platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine, PAF), a potent antihypertensive lipid produced by the kidney, may be decreased by hyperinsulinemia. The present study was designed to evaluate the effect of chronic hyperinsulinemia on renal PAF metabolism, arterial blood pressure and whole body insulin sensitivity. Chronic catheterized, unstressed rats were infused with saline or insulin plus glucose to create a chronic condition of sustained euglycemic (approximately 130 mg/dl) hyperinsulinemia (approximately 90 mU 1. or 3-fold over basal levels). PAF is a metabolically unstable compound being susceptible to rapid degradation to the biologically inactive lyso-PAF, a metabolite which also serves as a precursor for PAF synthesis. PAF synthesis and counter-regulatory prostaglandins may be derived from the same arachidonate precursor. The enzymes which catalyze these reactions were measured in plasma and in the subcellular fractions of the kidneys. Compared to saline-treated rats, sustained physiologic hyperinsulinemia for 7 days: (i) decreased insulin-mediated glucose disposal by 30%; (ii) caused an increased plasma PAF:acetylhydrolase, which degrades PAF to lyso-PAF, without any change in cytosolic PAF:acetylhydrolase activity; and (iii) completely inhibited microsomal lyso-PAF:acetyl CoA acetyltransferase activity which catalyzes the conversion of lyso-PAF back to bioactive PAF. The increased catabolism of PAF in plasma, combined with decreased renal PAF biosynthesis, would be expected to decrease circulating PAF levels leading to a rise in blood pressure. However, blood pressure remained unchanged. The sustained hyperinsulinemia stimulated plasma membrane CoA-independent transacylase activity, which is responsible for the mobilization of arachidonates into lyso-PAF, to form l-alkylarchidonoyl-glycerophosphocholine. The latter is the stored precursor for the synthesis of PAF and vasodilatory prostaglandins, which may have offset the effect of decreased PAF. We hypothesize that hyperinsulinemia may alter the blood pressure only if the balance between the synthesis/catabolism of PAF and vasodilatory prostaglandins is disrupted.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed1997

Plasma PAF acetylhydrolase in non-insulin dependent diabetes mellitus and obesity: effect of hyperinsulinemia and lovastatin treatment.

Insulin resistance is characterized principally by impaired insulin-mediated glucose uptake which provokes a compensatory increase in pancreatic beta-cell secretory activity. For a time this may produce well-controlled plasma glucose levels but as the insulin resistance worsens the augmented insulin production becomes inadequate to keep plasma glucose at euglycemia leading to the development of non-insulin dependent diabetes mellitus (NIDDM), accompanied by hyperinsulinemia and hyperglycemia. A number of metabolic defects are associated with NIDDM including obesity, hypercoagulability, cardiovascular disease risk factors such as hypertension and dyslipidemia and these constitute the insulin resistance syndrome. The identity of the biochemical factor that might link all these defects is not yet known. We have hypothesized that platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF) may be such a link. In this study, we measured plasma acetylhydrolase (EC.1.1.48), which degrades PAF to the inactive metabolise lyso-PAF, as a surrogate for PAF activity in three groups of hypercholesterolemic subjects: lean controls (n = 9), non-diabetic obese (n = 6) and NIDDM subjects (n = 6). The ages and body mass indices of the subjects were 46 +/- 3.1 and 24.2 +/- 2.2 for the lean controls, 52 +/- 2.5 and 28.7 +/- 0.9 for the NIDDM subjects and 60 +/- 2 and 27.6 +/- 2.1 for the obese, non-diabetic subjects (mean +/- S.E.M.). The measurements were made before and after therapy with the cholesterol-lowering drug lovastatin, a 3-hydroxy 3 methylglutaryl (HMG) coenzyme. A reductase inhibitor (40 mg/day) for 3 months. Fasting plasma glucose (FPG) levels were 91 +/- 11, 96 +/- 3 and 146 +/- 11 mg/dl, for the lean, obese and NIDDM subjects, respectively, before therapy began. Lovastatin did not affect FPG in any of the three subject groups. Before treatment, the fasting plasma insulin (FPI) levels were 6.1 +/- 0.92, 10.83 +/- 2.03 and 14.68 +/- 3.64 mU/l for the lean, non-diabetic obese and NIDDM subjects, respectively. After lovastatin therapy only the obese group exhibited a significant change in FPI (15.35 +/- 2.47 mU/l) (P < 0.05). Total cholesterol levels were similar in all three groups both before and after lovastatin therapy but within each group lovastatin therapy significantly reduced the total cholesterol by 32, 29 and 34% in the lean, obese and NIDDM subject groups respectively (P < 0.0001). Lovastatin therapy reduced LDL-cholesterol levels by 40, 32 and 46% in the lean, obese and NIDDM subjects, respectively, but produced no significant effect on HDL or triglyceride levels. Before therapy, the plasma acetylyhydrolase activities were 104 +/- 7, 164 +/- 7 and 179 +/- 7 nmol/ml per min in the lean, obese and NIDDM subjects, respectively. Lovastatin therapy reduced plasma acetylhydrolase levels to 70 +/- 7, 87 +/- 6 and 86 +/- 7 nmol/ml per min in the lean, obese and NIDDM subjects, respectively. Plasma acetylhydrolase activity was predominantly (> 80%) associated with LDL cholesterol both before and after lovastatin treatment. Also, plasma acetylhydrolase activity significantly correlated with fasting plasma insulin levels before lovastatin therapy but not after. Taken together, this study clearly implicates PAF metabolism in three defects associated with the insulin resistance syndrome: hypercholesterolemia, obesity and NIDDM. Additionally, we conclude that chronic hyperinsulinemia may play a significant role in the production of plasma acetylhydrolase.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed1997

Protein metabolism in human obesity: relationship with glucose and lipid metabolism and with visceral adipose tissue.

It is controversial whether metabolic disorders of human obesity include protein metabolism. Even less information is available concerning the effect of fat distribution on protein metabolism. Therefore, a comprehensive evaluation of glucose, lipid, and protein metabolism was performed in 11 obese nondiabetic and 9 normal women whose body composition and regional fat distribution were determined. [1-14C]Leucine and [3-3H]glucose were infused in the postabsorptive state and during an euglycemic hyperinsulinemic (35-40 microU/mL) clamp combined with indirect calorimetry for assessment of leucine flux, oxidation, and nonoxidative disposal, glucose turnover and oxidation, and lipid oxidation. Fat-free mass (FFM) was estimated by a bolus of 3H2O. Subcutaneous abdominal and visceral adipose tissues were determined by nuclear magnetic resonance imaging. During the clamp, obese women had lower glucose turnover (4.51 +/- 0.41 vs. 6.63 +/- 0.40 mg/min.kg FFM; P < 0.05), with a defect in both oxidation (3.27 +/- 0.22 vs. 3.89 +/- 0.21) and nonoxidative disposal (1.24 +/- 0.27 vs. 2.74 +/- 0.41; P < 0.005), whereas lipid oxidation was higher during the clamp (0.49 +/- 0.15 vs. 0.17 +/- 0.09 mg/min.kg FFM). There was no difference in leucine flux (basal, 2.23 +/- 0.17 vs. 2.30 +/- 0.29; clamp, 2.06 +/- 0.19 vs. 2.10 +/- 0.24 mumol/min.kg FFM), oxidation (basal, 0.37 +/- 0.04 vs. 0.36 +/- 0.05; clamp, 0.34 +/- 0.04 vs. 0.39 +/- 0.06) and nonoxidative leucine disposal (basal, 1.86 +/- 0.17 vs. 1.94 +/- 0.26; clamp, 1.72 +/- 0.20 vs. 1.71 +/- 0.19) in the two groups. In obese women, basal leucine oxidation was directly related with glucose oxidation and inversely to lipid oxidation (both P < 0.05), whereas visceral adipose tissue was inversely related to leucine flux both in the basal state and during the clamp (P < 0.05). In conclusion, in human obesity, 1) rates of protein metabolism in the basal state and in the range of insulin concentrations encountered after a meal are normal; 2) protein oxidation is positively related to glucose oxidation and negatively related to lipid oxidation; and 3) visceral adipose tissue is inversely related to all parameters of protein metabolism.

Adipose Tissue↗

PubMed1997

Seven days of euglycemic hyperinsulinemia induces insulin resistance for glucose metabolism but not hypertension, elevated catecholamine levels, or increased sodium retention in conscious normal rats.

Epidemiological studies have suggested an association among chronic hyperinsulinemia, insulin resistance, and hypertension. However, the causality of this relationship remains uncertain. In this study, chronically catheterized conscious rats were made hyperinsulinemic for 7 days (approximately 90 mU/l, i.e., threefold over basal), while strict euglycemia was maintained (approximately 130 mg/dl, coefficient of variation < 10%) by using a modification of the insulin/glucose clamp technique. Control rats received vehicle infusion. Baseline mean arterial pressure and heart rate were 125 +/- 5 mmHg and 427 +/- 12 beats/min and remained unchanged during the 7-day infusion of insulin (127 +/- 7 mmHg; 401 +/- 12 beats/min) or vehicle (133 +/- 4 mmHg; 411 +/- 10 beats/min). Baseline plasma epinephrine (88 +/- 15 pg/ml), norepinephrine (205 +/- 31 pg/ml), and sodium balance (0.34 +/- 0.09 mmol) remained constant during the 7-day insulin or vehicle infusion. After 7 days of insulin or vehicle infusion, in vivo insulin action was determined in all rats using a 2-h hyperinsulinemic (1 mU/min) euglycemic clamp with [3-3H]glucose infusion to quantitate whole-body glucose uptake, glycolysis, glucose storage (total glucose uptake minus glycolysis), and hepatic glucose production. Compared with vehicle-treated rats, 7 days of sustained hyperinsulinemia resulted in a reduction (P < 0.01) in insulin-mediated glucose uptake, glucose storage, and glycolysis by 39, 62, and 26%, respectively. Hepatic glucose production was normally suppressed after 7 days of hyperinsulinemia. Neither insulin-stimulated glucose uptake nor glucose storage correlated with blood pressure or heart rate. In conclusion, 7 days of euglycemic hyperinsulinemia induces severe insulin resistance with respect to whole-body glucose metabolism but does not increase blood pressure, catecholamine levels, or sodium retention. This indicates that hyperinsulinemia-induced insulin resistance is not associated with the development of hypertension in rats who do not have a genetic predisposition for hypertension. Because hyperinsulinemia was initiated in normal rats under euglycemic conditions, additional (inherited or acquired) factors may be necessary to observe an effect of hyperinsulinemia and/or insulin resistance to increase blood pressure.

Animals↗

PubMed1996

Insulin resistance and coronary artery disease.

The purpose of the present study was to quantitate insulin-mediated glucose disposal in normal glucose tolerant patients with angiographically documented coronary artery disease (CAD) and to define the pathways responsible for the insulin resistance. We studied 13 healthy, normal weight, normotensive subjects with angiographically documented CAD and 10 age-, weight-matched control subjects with an oral glucose tolerance test and a 2-h euglycaemic insulin (40 mU.m-2.min-1) clamp with tritiated glucose and indirect calorimetry. Lean body mass was measured with tritiated water. All CAD and control subjects had a normal oral glucose tolerance test. Fasting plasma insulin concentration (66 +/- 6 vs 42 +/- 6 pmol/l, p < 0.05) and area under the plasma insulin curve following glucose ingestion (498 +/- 54 vs 348 +/- 42 pmol.l-1.min-1, p < 0.001) were increased in CAD vs control subjects. Insulin-mediated whole body glucose disposal (27.8 +/- 3.9 vs 38.3 +/- 4.4 mumol.kg fat free mass (FFM)-1.min-1, p < 0.01) was significantly decreased in CAD subjects and this was entirely due to diminished non-oxidative glucose disposal (8.9 +/- 2.8 vs 20.0 +/- 3.3 mumol.kg FFM-1.min-1, p < 0.001). The magnitude of insulin resistance was positively correlated with the severity of CAD (r = 0.480, p < 0.05). In the CAD subjects basal and insulin-mediated rates of glucose and lipid oxidation were normal and insulin caused a normal suppression of hepatic glucose production. In conclusion, subjects with angiographically documented CAD are characterized by moderate-severe insulin resistance and hyperinsulinaemia and should be included in the metabolic and cardiovascular cluster of disorders that comprise the insulin resistance syndrome or "syndrome X'.

Blood Glucose↗

PubMed1996

A model to measure insulin effects on glucose transport and phosphorylation in muscle: a three-tracer study.

We studied five healthy subjects with perfused forearm and euglycemic clamp techniques in combination with a three-tracer (D-[12C]mannitol, not transportable; 3-O-[14C]methyl-D-glucose, transportable but not metabolizable; D-[3-3H]glucose, transportable and metabolizable) intra-arterial pulse injection to assess transmembrane transport and intracellular phosphorylation of glucose in vivo in human muscle. The washout curves of the three tracers were analyzed with a multicompartmental model. A priori identifiability analysis of the tracer model shows that the rate constants of glucose transport into and out of the cells and of glucose phosphorylation are uniquely identifiable. Tracer model parameters were estimated by a nonlinear least-squares parameter estimation technique. We then solved for the tracee model and estimated bidirectional transmembrane transport glucose fluxes, glucose intracellular phosphorylation, extracellular and intracellular volumes of glucose distribution, and extracellular and intracellular glucose concentrations. Physiological hyperinsulinemia (473 +/- 22 pM) caused 2.7-fold (63.1 +/- 7.2 vs. 23.4 +/- 6.1 mumol.min-1.kg-1, P < 0.01) and 5.1-fold (42.5 +/- 5.8 vs. 8.4 +/- 2.2 mumol.min-1.kg-1, P < 0.01) increases in transmembrane influx and intracellular phosphorylation of glucose, respectively. Extracellular distribution volume and concentration of glucose were unchanged, whereas intracellular distribution volume of glucose was increased (approximately 2-fold) and intracellular glucose concentration was almost halved by hyperinsulinemia. In summary, 1) a multicompartment model of three-tracer kinetic data can quantify transmembrane glucose fluxes and intracellular glucose phosphorylation in human muscle; and 2) physiological hyperinsulinemia stimulates both transport and phosphorylation of glucose and, in doing so, amplifies the role of glucose transport as a rate-determining step of muscle glucose uptake.

Adult↗

PubMed1996

Insulin and hyperaminoacidemia regulate by a different mechanism leucine turnover and oxidation in obesity.

Seven normal glucose-tolerant obese subjects [ideal body weight (IBW) = 161%] and 18 controls (IBW = 102%) were studied with the euglycemic insulin clamp (10 and 40 mU.m-2.min-1) technique, [14C]leucine infusion, and indirect calorimetry to examine if the insulin resistance with respect to glucose metabolism extends to amino acid/protein metabolism. In the basal state, total plasma amino acid and leucine concentrations, endogenous leucine flux (ELF), leucine oxidation (LO), and nonoxidative leucine disposal (NOLD) were similar in obese and control subjects. During both low (10 mU.m-2.min-1)- and higher (40 mU.m-2.min-1)-dose insulin clamp studies, insulin-mediated glucose uptake was reduced in obese vs. control subjects (P < 0.01). During the last hour of the higher-dose insulin clamp step, the decrease in total plasma amino acids, branched-chain amino acids, and leucine concentration was impaired in obese vs. control subjects (P < 0.01). However, suppression of ELF and NOLD was similar in both groups. During the low-dose insulin clamp, the decrease in plasma leucine concentration, LO, and ELF all were impaired (P < 0.01). A second study was performed in which the total plasma amino acid concentration was increased two- to threefold in both groups. Under these conditions of low plasma insulin/high amino acid levels, LO and NOLD increased similarly in obese and control subjects. In conclusion, insulin resistance is a common feature of both glucose and protein metabolism in obesity. The defect in protein metabolism is characterized by an impairment of the ability of insulin to inhibit proteolysis; the stimulatory effect of hyperaminoacidemia on protein synthesis is intact in obesity.

Adult↗

PubMed1996

Effect of alpha-adrenergic blockers, ACE inhibitors, and calcium channel antagonists on renal function in hypertensive non-insulin-dependent diabetic patients.

In the present study we investigated the effect of a selective alpha 1-adrenergic blocker (doxazosin), an angiotensin-converting enzyme (ACE) inhibitor (captopril), and a calcium channel antagonist (nifedipine) on renal function in hypertensive non-insulin-dependent diabetic patients. 30 NIDD hypertensive patients (age = 50 +/- 3 years; BMI = 30 +/- 1 kg/m2) (mean +/- SEM) were studied before and after a 12-week period of antihypertensive treatment. Ten patients were treated with doxazosin (Cardura) (2-8 mg once daily or 8 mg b.i.d.), 9 with captopril (Capoten) (25-50 mg b.i.d.), and 11 with nifedipine (Procardia-XL) (30-60 mg once daily). Blood pressure, creatinine clearance, 24-hour urinary protein excretion, fasting plasma glucose concentration and glycosylated hemoglobin were measured before and after drug treatment. Fasting plasma glucose and glycosylated hemoglobin (HbA1c) were similar in all three groups prior to the start of antihypertensive therapy and did not change significantly from baseline in any treatment groups. In the doxazosin group creatinine clearance rose from 99 +/- 8 to 122 +/- 8 ml/1.73 m2.min (p < 0.01), while 24-hour urinary protein excretion declined from 2.66 +/- 0.05 to 1.76 +/- 0.02 mg/day/ml/1.73 m2.min (p < 0.01). In diabetics treated with captopril creatinine clearance rose from 93 +/- 6 to 109 +/- 9 ml/1.73 m2.min (p < 0.05), while the 24-hour urinary protein excretion fell from 2.70 +/- 0.05 to 2.03 +/- 0.04 mg/day/ml/1.73 m2.min (p < 0.05). In patients treated with nifedipine creatinine clearance did not change (97 +/- 6 vs. 94 +/- 7 ml/1.73 m2.min), while 24-hour urinary protein excretion decreased from 2.84 +/- 0.04 to 1.95 +/- 0.03 mg/day/ml/1.73 m2.min. Systolic and diastolic blood pressure were similar in doxazosin (150 +/- 3/95 +/- 2 mm Hg), captopril (153 +/- 3/93 +/- 1), and nifedipine (155 +/- 4/93 +/- 1) groups prior to the start of antihypertensive therapy and declined to 143 +/- 3/84 +/- 3 (doxazosin), 139 +/- 3/82 +/- 3 (captopril), and 141 +/- 3/84 +/- 1 (nifedipine) mm Hg (all p < 0.01 vs. pretreatment). In summary, both doxazosin and captopril treatment were associated with significant rises in GFR, while all three antihypertensive agents caused a significant decline in proteinuria. These results indicate that alpha-adrenergic blockers, ACE inhibitors, and calcium channel antagonists can safely and effectively be used in the clinical management of non-insulin-dependent diabetic patients with hypertension.

Adrenergic alpha-Antagonists↗

PubMed1996

Metabolic effects of metformin on glucose and lactate metabolism in noninsulin-dependent diabetes mellitus.

Metformin is a biguanide that has been shown to effectively lower plasma glucose levels in subjects with noninsulin-dependent diabetes mellitus (NIDDM). However, its mechanism of action remains unknown. Studies that have examined the effect of metformin on hepatic glucose production (HGP) and muscle glucose utilization in NIDDM have yielded conflicting results, and little information is available about the action of metformin on lactate turnover and gluconeogenesis from lactate in humans. We studied 20 NIDDM subjects and 8 nondiabetic controls in a randomized, double blind, placebo-controlled trial to determine the effect of 15 weeks of treatment with metformin or placebo on glucose and lactate metabolism. Before and after treatment, all participants received a 7-h infusion of [6-3H]glucose and [3-14C]lactate in combination with indirect calorimetry and estimation of lactate central vein specific activity. A euglycemic insulin clamp (20 mU/m2.min) was performed during the last 3 h of the tracer infusions. The study design allowed us to evaluate the effects of metformin vs. placebo treatment on glycemic control, plasma lipid profile, HGP, insulin-mediated glucose uptake, oxidative and nonoxidative glucose metabolism, and lactate turnover. Metformin treatment significantly reduced fasting plasma glucose (196 +/- 18 vs. 152 +/- 12 mg/dL; P < 0.01), hemoglobin A1 (12.5 +/- 0.6 vs. 9.2 +/- 0.3%; P < 0.01), and plasma triglyceride and low density lipoprotein cholesterol concentrations. When diabetics were compared to nondiabetic controls, basal HGP was higher (12.9 +/- 1.0 vs. 9.8 +/- 1.2 mumol/kg.min; P < 0.01) despite the presence of fasting hyperinsulinemia and insulin-mediated total body glucose disposal (10.9 +/- 0.9 vs. 20.2 +/- 3.3 mumol/kg.min; P < 0.01) was decreased. Metformin significantly reduced fasting HGP (from 12.9 +/- 0.7 to 11.0 +/- 0.5 mumol/kg.min; P < 0.01), but did not enhance total body glucose disposal during insulin stimulation (10.9 +/- 0.9 vs. 11.0 +/- 0.5 mumol/kg.min; P = NS). Neither oxidative nor nonoxidative glucose disposal was improved by metformin treatment. The fasting plasma lactate concentration (1.1 +/- 0.1 vs. 0.6 +/- 0.1 mmol/L) and lactate turnover (14.0 +/- 0.8 vs. 10.3 +/- 0.6 mumol/kg.min) were significantly increased in diabetics and strongly correlated (r = 0.68; P < 0.001). The percent gluconeogenesis derived from lactate was similar in diabetic and control subjects (17 +/- 2% vs. 15 +/- 2%; P = NS), but the estimated rate of gluconeogenesis from lactate was increased in the diabetic group (P < 0.01). Despite the significant reduction in HGP after metformin treatment, the percentage of gluconeogenesis from lactate and the rate of lactate-derived gluconeogenesis were unchanged from baseline. Basal lactate turnover (15.4 +/- 1.4 vs. 14.8 +/- 1.4 mumol/kg.min) and lactate oxidation (7.9 +/- 0.7 vs. 8.1 +/- 0.9 mumol/ kg.min) as well as total lactate turnover and lactate oxidation during the insulin clamp were similar before and after metformin treatment. There were no changes in any of the above metabolic parameters in the placebo-treated group. In poorly controlled NIDDM subjects, the primary mechanism by which metformin improves glycemic control is related to the suppression of accelerated basal HGP, and this most likely is secondary to an inhibition of hepatic glycogenolysis. Metformin has no effect on the rate of lactate turnover or gluconeogenesis from lactate in either the basal or insulin-stimulated states.

Blood Glucose↗

PubMed1996

Increased glutamine:fructose-6-phosphate amidotransferase activity in skeletal muscle of patients with NIDDM.

Overactivity of the hexosamine pathway mediates glucose-induced insulin resistance in rat adipocytes. Glutamine:fructose-6-phosphate amidotransferase (GFA) is the rate-limiting enzyme of this pathway. We determined GFA activity in human skeletal muscle biopsies and rates of insulin-stimulated whole-body, oxidative, and nonoxidative glucose disposal using the euglycemic insulin clamp technique combined with indirect calorimetry (insulin infusion rate (1.5 mU x kg-1 x min-1)) in 12 male patients with NIDDM (age 54 +/- 2 years, BMI 27.5 +/- 0.9 kg/m2, fasting plasma glucose 8.5 +/- 0.6 mmol/l) and 9 matched normal men. GFA activity was detectable in human skeletal muscles and completely inhibited by uridine-5'-diphospho-N-acetylglucosamine (UDP-GlcNAc) in all subjects. GFA activity was 46% increased in the NIDDM patients compared with the normal subjects (9.5 +/- 1.3 vs. 6.5 +/- 1.2 pmol, P < 0.05). Whole-body glucose uptake was 58% decreased in patients with NIDDM (20 +/- 3 micromol x kg body wt-1 x min-1) compared with normal subjects (47 +/- 4 micromol x kg body wt-1 x min-1, P < 0.001). This decrease was attributable to decreases in both glucose oxidation (9 +/- 1 vs. 15 +/- 1 micromol x kg-1 x min-1, NIDDM patients vs. control subjects, P < 0.002) and nonoxidative glucose disposal (11 +/- 2 vs. 31 +/- 4 micromol x kg-1 x min-1, P < 0.001). In patients with NIDDM, both HbA1c (r= 0.51, P < 0.05) and BMI (r= -0.57, P < 0.05) correlated with whole-body glucose uptake. HbA1c but not BMI or insulin sensitivity was correlated with basal GFA activity (r = -0.57,P < 0.01) in NIDDM patients and control subjects. We conclude that GFA is found in human skeletal muscle and that all this activity is sensitive to feedback inhibition by UDP-GlcNAc. Chronic hyperglycemia is associated with an increase in skeletal muscle GFA activity, suggesting that increased activity of the hexosamine pathway may contribute to glucose toxicity and insulin resistance in humans.

Blood Glucose↗

PubMed1996

Differential responsiveness of protein synthesis and degradation to amino acid availability in humans.

We investigated the effects of graded hyperaminoacidemia on protein metabolism in eight healthy, young (25 +/- 2 years), normal weight (BMI = 25 +/- 1 kg/m2), overnight-fasted human subjects. A balanced amino acid solution was infused for 180 min at five different rates: 0.5 (study I), 1.0 (study II), 2.0 (study III), 4.0 (study IV). and 6.0 (study V) mg x kg-1 x min-1 on separate days in random order. Studies were performed with [1-14C]leucine infusion and indirect calorimetry to calculate leucine oxidation (LOX), nonoxidative leucine disposal (NOLD) (an index of protein synthesis), and endogenous leucine flux (ELF) (an index of proteolysis). Basal total plasma amino acid concentrations averaged 1.85 +/- 0.1 mmol/l and increased to 2.27 +/- 0.1, 2.70 +/- 0.2, 3.84 +/- 0.2, 5.87 +/- 0.4, and 7.52 +/- 0.3 mmol/l in studies I-V, respectively. ELF decreased from a basal value of 2.27 +/- 0.2 to 2.12 +/- 0.2, 1.97 +/- 0.1, 1.73 +/- 0.2, 1.67 +/- 0.3, and 1.65 +/- 0.1 micromol x kg-1 x min-1 in studies I-V, respectively (P < 0.05 for study I vs. basal, P < 0.01 for studies II-V vs. basal, and NS for studies IV and V vs. study III). LOX increased from a basal value of 0.31 +/- 0.04 to 0.38 +/- 0.05, 0.41 +/- 0.02, 0.64 +/- 0.04, 1.11 +/- 0.07, and 1.56 +/- 0.05 micromol x kg-1 x min-1 in studies I-V (all P < 0.01 vs. basal; P < 0.05-0.01 for each study vs. preceding study). Basal NOLD averaged 1.96 +/- 0.2 and did not change significantly in studies I and II (2.03 +/- 0.2 and 2.10 +/- 0.1 micromol x kg-1 x min-1). In contrast, a significant increase in NOLD was observed in studies III, IV, and V (to 2.3 +/- 0.15, 2.74 +/- 0.2, and 3.25 +/- 0.7 micromol x kg-1 x min-1, respectively; all P < 0.01 vs. basal; P < 0.05-0.01 for each study vs. preceding study). The net leucine balance (difference between ELF and NOLD)(-0.31 +/- 0.06 micromol x kg-1 x min-1) became less negative in study I (P < 0.01 vs. basal) and positive during studies II-V when the rise in plasma total amino acid levels was >/= 50% above basal level (P < 0.01 vs. each preceding study). In conclusion, NOLD, ELF, and LOX exhibit a differential responsiveness to acute changes in substrate availability: 1) small increments (25-50%) in plasma amino acid levels inhibit ELF and stimulate LOX but have no effect on NOLD; 2) stimulation of NOLD is observed only with increments in plasma amino acid levels >/= 100% above basal values; and 3) increments in plasma amino acid concentrations > 100% above basal values cause a progressive dose-related increase in LOX and NOLD but do not induce any further inhibition of ELF.

Adult↗

PubMed1996

Roles of glucose transport and glucose phosphorylation in muscle insulin resistance of NIDDM.

Insulin resistance for glucose metabolism in skeletal muscle is a key feature in NIDDM. The quantitative role of the cellular effectors of glucose metabolism in determining this insulin resistance is still imperfectly known. We assessed transmembrane glucose transport and intracellular glucose phosphorylation in vivo in skeletal muscle in nonobese NIDDM patients. We performed euglycemic insulin clamp studies in combination with the forearm balance technique (brachial artery and deep forearm vein catheterization) in five nonobese NIDDM patients and seven age- and weight-matched control subjects (study 1). D-Mannitol (a nontransportable molecule), 3-O-[14C]methyl-D-glucose (transportable, but not metabolizable) and D[3-3H]glucose (transportable and metabolizable) were simultaneously injected into the brachial artery, and the washout curves were measured in the deep venous effluent blood. In vivo rates of transmembrane transport and intracellular phosphorylation of D-glucose in forearm muscle were determined by analyzing the washout curves with the aid of a multicompartmental model of glucose kinetics in forearm tissues. At similar steady-state concentrations of plasma insulin (approximately 500 pmol/l) and glucose (approximately 5.0 mmol/l), the rates of transmembrane influx (34.3 +/- 9.1 vs. 58.5 +/- 6.5 micromol x min(-1) x kg(-1), P < 0.05) and intracellular phosphorylation (5.4 +/- 1.6 vs. 38.8 +/- 5.1 micromol x min(-1) x kg(-1), P < 0.01) in skeletal muscle were markedly lower in the NIDDM patients than in the control subjects. In the NIDDM patients (study 2), the insulin clamp was repeated at hyperglycemia, (approximately 13 mmol/l) trying to match the rates of transmembrane glucose influx measured during the clamp in the controls. The rate of transmembrane glucose influx (62 +/- 15 micromol x min(-1) x kg(-1)) in the NIDDM patients was similar to the control subjects, but the rate of intracellular glucose phosphorylation (16.6 +/- 7.5 micromol x min(-1) x kg(-1)), although threefold higher than in the patients during study 1 (P < 0.05), was still approximately 60% lower than in the control subjects (P < 0.05). These data suggest that when assessed in vivo, both transmembrane transport and intracellular phosphorylation of glucose are refractory to insulin action and add to each other in determining insulin resistance in skeletal muscle of NIDDM patients. It will be of interest to compare the present results with the in vivo quantitation of the initial rate of muscle glucose transport when methodology to perform this measurement becomes available.

3-O-Methylglucose↗

PubMed1996

The GENNID Study. A resource for mapping the genes that cause NIDDM.

OBJECTIVE: To develop a resource, consisting of comprehensive data and lymphoblastoid cell lines, of well-characterized NIDDM families that will be available to the scientific community for genetic studies of NIDDM. RESEARCH DESIGN AND METHODS: Non-Hispanic white, Hispanic, African-American, and Japanese-American multiplex NIDDM families, with a minimum of one affected sib-pair, are being collected by the eight Harold Rifkin Family Acquisition Centers. Detailed family and medical histories are obtained from all participants. Family members with diabetes have fasting blood samples drawn, while nondiabetic family members have an oral glucose tolerance test and, when possible, insulin sensitivity and insulin secretion measurements by frequently sampled intravenous glucose tolerance testing or euglycemic insulin clamp. Lymphoblastoid cell lines are established for all participants. RESULTS: Over 1,400 individuals from approximately 220 families have been studied since the start of the GENNID (Genetics of NIDDM) program in July 1993. The goal is that by July 1997, data from 300 non-Hispanic white families, > 100 Hispanic families, > 100 African-American families, and 15 Japanese-American families will have been collected. CONCLUSIONS: The identification of the genes responsible for NIDDM may now be achievable, but only if sound phenotypic data are linked to genetic material from a large number of well-described multiplex families. The GENNID project of the American Diabetes Association is creating a comprehensive resource that will expedite the identification of the genetic basis of NIDDM.

Black or African American↗

PubMed1995

Efficacy of metformin in patients with non-insulin-dependent diabetes mellitus. The Multicenter Metformin Study Group.

BACKGROUND: Sulfonylurea drugs have been the only oral therapy available for patients with non-insulin-dependent diabetes mellitus (NIDDM) in the United States. Recently, however, metformin has been approved for the treatment of NIDDM. METHODS: We performed two large, randomized, parallel-group, double-blind, controlled studies in which metformin or another treatment was given for 29 weeks to moderately obese patients with NIDDM whose diabetes was inadequately controlled by diet (protocol 1: metformin vs. placebo; 289 patients), or diet plus glyburide (protocol 2: metformin and glyburide vs. metformin vs. glyburide; 632 patients). To determine efficacy we measured plasma glucose (while the patients were fasting and after the oral administration of glucose), lactate, lipids, insulin, and glycosylated hemoglobin before, during, and at the end of the study. RESULTS: In protocol 1, at the end of the study the 143 patients in the metformin group, as compared with the 146 patients in the placebo group, had lower mean (+/- SE) fasting plasma glucose concentrations (189 +/- 5 vs. 244 +/- 6 mg per deciliter [10.6 +/- 0.3 vs. 13.7 +/- 0.3 mmol per liter], P < 0.001) and glycosylated hemoglobin values (7.1 +/- 0.1 percent vs. 8.6 +/- 0.2 percent, P < 0.001). In protocol 2, the 213 patients given metformin and glyburide, as compared with the 210 patients treated with glyburide alone, had lower mean fasting plasma glucose concentrations (187 +/- 4 vs. 261 +/- 4 mg per deciliter [10.5 +/- 0.2 vs. 14.6 +/- 0.2 mmol per liter], P < 0.001) and glycosylated hemoglobin values (7.1 +/- 0.1 percent vs. 8.7 +/- 0.1 percent, P < 0.001). The effect of metformin alone was similar to that of glyburide alone. Eighteen percent of the patients given metformin and glyburide had symptoms compatible with hypoglycemia, as compared with 3 percent in the glyburide group and 2 percent in the metformin group. In both protocols the patients given metformin had statistically significant decreases in plasma total and low-density lipoprotein cholesterol and triglyceride concentrations, whereas the values in the respective control groups did not change. There were no significant changes in fasting plasma lactate concentrations in any of the groups. CONCLUSIONS: Metformin monotherapy and combination therapy with metformin and sulfonylurea are well tolerated and improve glycemic control and lipid concentrations in patients with NIDDM whose diabetes is poorly controlled with diet or sulfonylurea therapy alone.

Blood Glucose↗

PubMed1995

Comparison of the effects of human recombinant insulin-like growth factor I and insulin on plasma amino acid concentrations and leucine kinetics in humans.

We examined the effects of recombinant human insulin-like growth factor I (IGF-I) and insulin on the plasma amino acid (AA) profile and leucine kinetics in eight normal subjects. IGF-I was infused at 52 pmol.kg-1.min-1, in combination with prime-continuous [1-14C] leucine infusion, to obtain steady-state plasma concentrations of total (54 +/- 3 nmol/l) and free (7.3 +/- 1 nmol/l) IGF-I (study 1). In response to IGF-I, plasma AA levels declined by 37 +/- 3% (1975 +/- 198 to 1368 +/- 120 mumol/l) and total branched chain amino acids (BCAA) declined by 34 +/- 3% (390 +/- 21 to 256 +/- 13 mumol/l). This hypoaminoacidaemic effect was associated with a decline in endogenous leucine flux of 17 +/- 2% (1.88 +/- 0.05 to 1.57 +/- 0.04 mumol.kg-1.min-1) and leucine oxidation of 17 +/- 1% (0.31 +/- 0.02 vs 0.26 +/- 0.02 mumol.kg-1.min-1) (both p < 0.01 vs basal). The same subjects underwent a second study (study 2) in which insulin was infused at 6.22 pmol.kg-1.min-1 to obtain a steady-state plasma insulin concentration of 530 +/- 25 pmol/l while maintaining euglycaemia. The infusion rate was designed to match the declines in plasma BCAA levels and leucine turnover observed during IGF-I infusion. The rates of glucose infusion necessary to maintain euglycaemia during IGF-I and insulin infusion were 4.9 +/- 1.0 and 7.8 +/- 0.6 mg.kg-1.min-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

A novel mechanism of glipizide sulfonylurea action: decreased metabolic clearance rate of insulin.

To examine whether sulfonylureas inhibit the metabolic clearance rate (MCR) of insulin, 19 healthy young subjects participated in two experiments. In the first protocol (n = 10), a 3-h oral glucose load was performed with and without 2 mg of glipizide given 30 min before glucose ingestion. The total insulin response was 60% greater with than without glipizide (5.9 +/- 0.6 vs 3.7 +/- 0.5 microU/ml; P < 0.001). However, the total C-peptide responses were virtually identical (4.7 +/- 0.5 vs 4.8 +/- 0.4 nmol/l) in both studies. In the second protocol (n = 9), the MCR of insulin was measured during 4-h euglycemic insulin clamps performed with and without glipizide. In the study with glipizide, the subjects ingested 5 mg of glipizide at 120 min. The steady-state plasma insulin concentration during the 4th h, i.e., 1-2 h after glipizide ingestion, was significantly higher than during the 2nd h, i.e., before glipizide ingestion (99 +/- 22 vs 78 +/- 17 microU/ml; P < 0.01). In addition, glucose uptake during the 4th h was greater (8.0 +/- 1.6 vs 6.4 +/- 1.5 mg/kg.min) and the MCR of insulin was reduced (503 +/- 126 vs 621 +/- 176 ml/m2.min; P < 0.01). We conclude that glipizide augments plasma insulin levels both by enhancing its secretion and by decreasing the MCR of insulin.

Adult↗

PubMed1995

Is it possible to derive a reliable estimate of human visceral and subcutaneous abdominal adipose tissue from simple anthropometric measurements?

The aim of the study was to generate equations predicting visceral (VAT) and subcutaneous (SAT) abdominal adipose tissue (AT) from simple anthropometric measurements. Magnetic resonance imaging (MRI) was used to measure VAT and SAT cross-sectional areas at the level of L4 in 49 subjects (19 men and 30 women) with a large range of age and body mass index (BMI). BMI, waist and hip circumferences, waist to hip ratio (WHR), subscapular and paraumbilical skinfolds (i.e., "simple" anthropometric measurements), total body fat content by the isotope-dilution method, and abdominal sagittal diameter by MRI (i.e., "nonsimple" anthropometric measurements) were also measured. Equations to estimate VAT and SAT from age and simple anthropometric measurements (i.e., excluding total body fat and abdominal sagittal diameter) were developed. These equations were then used in 24 subjects (nine men and 15 women) to cross-validate them. The best regression equations, including waist circumference in men and waist circumference and age in women, explained 56% and 68% of VAT variability, respectively. The corresponding standard error of the estimate (SEE) in men was approximately 40% and in women approximately 37% of the mean value of VAT measured by MRI. The best regression equations developed to predict SAT had a higher explained variability (approximately 87% in both men and women) and a lower SEE (< 20% of the mean values of SAT measured by MRI). In men, the equation included BMI and hip circumference, and in women, BMI and age. The inclusion of a higher number of simple anthropometric parameters in the predictive models neither significantly increased the explained variability of VAT or SAT nor significantly decreased the SEE of VAT or SAT. Also, inclusion in the multiple regression analysis of total body fat content and abdominal sagittal diameter did not improve prediction. In the cross-validation study, differences between predicted and observed values of VAT were large, with a tendency to overestimation in both men and women. In contrast, differences between predicted and observed values of SAT were small. We suggest that SAT but not VAT can be estimated from age and simple anthropometric measurements. Direct methods (MRI, computed tomography [CT], or other options) should be used for assessment of VAT.

Abdomen↗