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P Wallace
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Evidence that glucose transport is rate-limiting for in vivo glucose uptake.
To determine whether glucose transport or intracellular glucose metabolism is rate-limiting for in vivo glucose uptake, rates of glucose disposal were measured in a group of normal subjects at varying levels of hyperglycemia designed to attain saturating rates of glucose disposal at low and high physiological insulin concentrations. At insulin levels of approximately 200 pmol/L, glucose disposal rates were 2.9 +/- 0.4, 4.7 +/- 0.5, 6.4 +/- 0.6, and 6.5 +/- 0.8 mg/kg/min at plasma glucose concentrations of 5.55, 11.10, 13.88, and 19.43 mmol/L (or 100, 200, 250, and 350 mg/dL, respectively). At insulin levels of approximately 750 pmol/L, glucose disposal rates were 1.7 to 2.1-fold higher: 6.2 +/- 0.7, 9.2 +/- 1.1, 11.0 +/- 1.1, and 12.3 +/- 1.4 mg/kg/min at glucose levels of 5.55, 11.10, 13.88, and 19.43 mmol/L. Thus, during both the 15- and 40-mU/m2/min insulin infusions, glucose disposal increased in a linear fashion from 5.55 to 13.88 mmol/L (r = .90) and then effectively plateaued at the same plasma glucose level. If the plateau of glucose disposal during the 40-mU/m2/min insulin infusion was due to saturation of the intracellular capacity to metabolize glucose, then when plasma glucose was increased from 13.88 to 19.43 mmol/L at the lower insulin level, the glucose disposal should have continued to increase and not plateau, since the rate of glucose disposal was only approximately 50% of that attained at the higher insulin infusion rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Synergistic anti-nociceptive effect of L-NG-nitro arginine methyl ester (L-NAME) and flurbiprofen in the mouse.
1. L-NG-nitro arginine methyl ester (L-NAME) administered i.p. produces anti-nociception in the mouse assessed by the formalin-induced paw licking and acetic acid-induced abdominal constriction models. The non-steroidal anti-inflammatory drug (NSAID), flurbiprofen, was similarly anti-nociceptive in both models. 2. Combination of a sub-threshold dose of L-NAME (10 mg kg-1) with increasing doses of flurbiprofen (25- 75 mg kg-1) or a sub-threshold dose of flurbiprofen (50 mg kg-1) with increasing doses of L-NAME (10- 100 mg kg-1) resulted in potentiated anti-nociception in the formalin model. Combined therapy with sub-threshold doses of L-NAME (10 mg kg-1) and indomethacin (10 mg kg-1) also resulted in significant anti-nociception. In addition, combining sub-threshold doses of L-NAME (12.5 mg kg-1) and flurbiprofen (2 mg kg-1) significantly reduced acetic acid-induced abdominal constriction. 3. L-NAME (10 mg kg-1) administered i.p. caused a significant (approximately 35%) increase in MAP in the urethane-anaesthetized mouse. Flurbiprofen (50 mg kg-1) was inactive. Combination treatment with L-NAME (10 mg kg-1) and flurbiprofen (50 mg kg-1) failed to elevate MAP above that observed with L-NAME alone. Neither L-NAME (10 mg kg-1) nor flurbiprofen (50 mg kg-1) either alone or in combination significantly altered mouse locomotor activity. 4. These results suggest that L-NAME and flurbiprofen/indomethacin act synergistically in their anti-nociceptive action in the mouse. Combination therapy with L-NAME and flurbiprofen and a similar NSAID may provide an alternative to the clinical control of pain in man.
An investigation of some S-nitrosothiols, and of hydroxy-arginine, on the mouse anococcygeus.
1. The effect of five S-nitrosothiols, and of the stereoisomers of NG-hydroxy-arginine (HOARG), were investigated on the mouse anococcygeus. 2. All five S-nitrosothiols produced concentration-related (0.1-100 microM) relaxations of carbachol (50 microM)-induced tone; the order of potency was S-nitroso-L-cysteine (CYSNO) > S-nitroso-N-acetyl-D,L-penicillamine (SNAP) > S-nitrosoglutathione (GSNO) > S-nitrosocoenzyme A (CoASNO) > S-nitroso-N-acetyl-L-cysteine (NACNO). The relaxations were unaffected by the nitric oxide synthase (NOS) inhibitor, L-NG-nitro-arginine (10 microM) (L-NOARG). 3. Cold-storage of the tissue for 72 h resulted in loss of sympathetic and non-adrenergic, non-cholinergic (NANC) nerve function. NOS activity in the tissue was reduced by 97%. Despite this, relaxations induced by the S-nitrosothiols were unaffected. 4. Haemoglobin (50 microM) attenuated relaxations induced by NO and the S-nitrosothiols, although responses to 3-isobutyl-1-methyl-xanthine were unaffected. N-methyl-hydroxylamine (2 mM) which has been shown previously to produce selective inhibition of NANC and nitrovasodilator responses in this tissue, also reduced responses to all S-nitrosothiols. 5. Hydroquinone (100 microM) greatly reduced relaxations to CYSNO (by 88%) but had no effect on those to SNAP, GSNO, CoASNO or NACNO. Since hydroquinone does not reduce responses to NANC stimulation, CYSNO is unlikely to be the NANC transmitter. 6. L-HOARG by itself (up to 100 microM) had no significant effect on carbachol-induced tone or on NANC (10 Hz; 10 strain every 100 s) relaxations. However, it produced reversal of the inhibitory effects of L-NOARG (10;pM), being only slightly less potent than L-arginine. D-HOARG was without effect.L-HOARG had no effect on relaxations induced by 1.51iM NO.7. The results show that S-nitrosothiols are potent relaxants of the mouse anococcygeus; they act directly on the smooth muscle with a mechanism similar to NO and other nitrovasodilators. In addition,the results are consistent with L-HOARG being an intermediate in the biosynthesis of NO from L-arginine, although there is no evidence for it acting to stabilize NO extracellularly.
Metabolic effects of new oral hypoglycemic agent CS-045 in NIDDM subjects.
OBJECTIVE: To study the metabolic effects of a new oral antidiabetic agent, CS-045, in subjects with non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS: Eleven NIDDM subjects (mean age 59 yr and body mass index 32.3) were treated with 400 mg/day CS-045 for 6-12 wk. Patients were hospitalized before and at the end of the drug-treatment period for metabolic studies, including oral glucose tolerance test (OGTT), meal tolerance test (MTT), euglycemic glucose-clamp studies, and lipid analyses. RESULTS: Eight subjects showed a marked clinical response to the drug, whereas 3 were nonresponders. The data were analyzed both for the total group and for the responders. Fasting plasma glucose (FPG) fell from 12.5 +/- 0.7 to 10.7 +/- 1.0 mM in the total group but fell more dramatically from 12.7 +/- 0.5 to 8.3 +/- 0.6 mM in the responder group. The area under the OGTT glucose curve improved by 17% in the total group and by 29% in the responders. The area under the MTT glucose curve improved by 38 and 52%, respectively. MTT levels of insulin, free fatty acids, and glucagon were significantly lower after treatment. Glucose disposal rates during glucose-clamp studies were increased in all subjects after CS-045 treatment. Mean increases were 63% at 120 mU.m-2.min-1 and 41% at 300 mU.m-2.min-1. Basal hepatic glucose production fell by 17% in the total group and by 28% in the responders. CONCLUSIONS: CS-045 improves insulin resistance, reduces insulinemia, lowers hepatic glucose production, and improves both fasting and postprandial glycemia in NIDDM subjects. CS-045 may represent a new therapeutic option for NIDDM.
Characterization of mucin glycoprotein-specific translation products from swine and human trachea, pancreas and colon.
RNA was isolated from cultured swine trachea epithelial cells and mucus-secreting tumor cell lines from human pancreas, lung and colon by extraction with guanidine isothiocyanate. Poly(A)+mRNA rich fractions were purified by repeated chromatography on oligo (dT)-cellulose columns and they were translated in a cell-free rabbit reticulocyte system. Translation products labelled with 35S-methionine were isolated by immunoprecipitation with specific antibodies to the polypeptide chains of mucin glycoproteins and they were analyzed by SDS-PAGE and fluorography. A single principal polypeptide band of 67 kDa was found in all cases when the immunoprecipitates were washed with buffer containing bovine serum albumin and unlabeled deglycosylated mucin glycoprotein. The intensity of the 67 kDa band decreased when unlabeled deglycosylated mucin glycoprotein was added to the translation mixture before immunoprecipitation. Affinity purified monospecific antibodies elicited against chemically deglycosylated polypeptide chains of purified mucin glycoproteins from human and swine trachea and Cowper's gland were all equally effective in immunoprecipitating the 67 kDa translation product. Monospecific antibodies directed against the glycosylated and unglycosylated regions of the polypeptide chain yielded single bands with a molecular size of 67 kDa in each case. Peptide profiles obtained by digestion of the 67 kDa translation product with S. aureus V-8 protease were identical to those obtained with deglycosylated human and swine trachea mucin glycoproteins. These studies clearly demonstrate that the translation product of swine trachea and human lung, colon and pancreatic mucin glycoprotein gene is a single polypeptide chain of 67 kDa. The relative size and properties of the translation products synthesized with poly (A)+RNA isolated from mucus-secreting cells derived from three different tissues are similar to those of mucin glycoproteins purified directly from mucus secretions of human and swine trachea epithelium.
Blood groups, secretor status and salivary Lewis, Lewis and 19.9 antigen levels in alcoholics and ethnic origin-matched controls.
Blood group and secretor status were determined in 89 heavy drinkers receiving outpatient treatment at a district general hospital in north-west London, and compared with 89 age-, sex- and ethnic origin-matched controls drawn from a panel of 1700 patients from a contiguous general practice. There were no significant differences in the distribution of ABO types and secretor status in the two groups. Differences in salivary mucins were investigated by assaying levels of sialylated and non-sialylated Lewis antigens and blood group antigens ABH in both patients and controls. Although there were no differences in the mean antigen levels for H, A, B Le(a) and Le(b) antigens, using the monoclonal antibody 19.9 (to sialylated Lewis(a) antigen), higher levels were found for groups O and B/AB non-secretors and for group A secretors in alcoholics compared with controls. In addition, inappropriate Le(a) and 19.9 immuno-reactivities were detected in the saliva samples of a group O Le(a)-b- secretor alcoholic and a group A Le(a)-b- secretor alcoholic, respectively. It is suggested that these changes in glycosylation of salivary proteins relate to the increased parotid gland cell proliferation known to occur in chronic alcoholics.
L-NG-nitro arginine methyl ester exhibits antinociceptive activity in the mouse.
1. L-NG-nitro arginine methyl ester (L-NAME, 1-75 mg kg-1) administered intraperitoneally (i.p.) elicits dose-related antinociception in the mouse assessed by the formalin-induced paw licking procedure. Antinociceptive activity is still present 24 h after injection. L-NAME (75 mg kg-1, i.p.) is also antinociceptive in the acetic acid-induced abdominal constriction and hot plate procedures. 2. L-NAME additionally produces a dose-related inhibition of formalin-induced paw licking following intracerebroventricular (i.c.v., 0.1-100 microgram per mouse) and oral (p.o., 75-150 mg kg-1) administration. 3. L-Arginine (600 mg kg-1, i.p.) but not D-arginine (600 mg kg-1) or naloxone (5 mg kg-1) reverses the antinociceptive effect of L-NAME in the formalin test. 4. High doses of L-NAME (37.5-600 mg kg-1) but not D-NAME (75 mg kg-1) administered i.p. produce dose-related increases in blood pressure of the urethane-anaesthetized mouse whilst i.c.v. injected L-NAME (0.1 and 100 microgram per mouse) in inactive. 5. L-NAME (75 mg kg-1, i.p.) did not inhibit oedema formation in the formalin-injected mouse hindpaw. 6. L-NAME (75 mg kg-1) did not produce any overt behavioural changes in treated mice and failed to influence locomotor activity or the incidence of dipping, crossing, rearing or circling behaviour assessed by a modified 'head-dipping' board procedure. A high dose of L-NAME (600 mg kg-1) reduced dipping behaviour and locomotor activity suggesting a possible sedative effect. D-NAME (600mgkg 1) was inactive. 7. These results suggest that L-NAME produces an opioid-independent and long-lasting antinociception in the mouse most probably by a direct effect within the central nervous system.
The effect of preceptorship upon diploma program nursing students' transition to the professional nursing role.
This quasi-experimental study determined the effect of a 17-week pregraduate preceptorship program upon diploma nursing students' (N = 22) performance of the professional nursing role. Nine students participated in the preceptorship program; 13 received the standard pregraduate clinical experience. Nursing performance was measured using Schwirian's Six Dimension Scale of Nursing Performance prior to, during, and upon completion of the pregraduate clinical experience. Based on the faculty adviser's appraisals, the preceptorship program was associated with significantly greater improvements in nursing performance within the teaching/collaboration and planning/evaluation dimensions.
Prevalence of fetal alcohol syndrome largely unknown.
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Long term survival after intensive care.
OBJECTIVE: To examine the long term survival of critically ill patients admitted to an intensive therapy unit and to ascertain the effects of age, severity of illness, and diagnostic category at admission on survival. DESIGN: Retrospective observational study with prospectively gathered data on all patients admitted to the unit between June 1985 and July 1987 and followed up until 1 January 1989. SETTING: Regional intensive therapy unit. PATIENTS: 513 critically ill adult patients, 16 of whom were excluded because measurements on severity of illness scoring were not available. MAIN OUTCOME MEASURES: Age, severity of illness (determined with the acute physiology and chronic health evaluation (APACHE) II score), and diagnostic category on admission; deaths in the unit; and long term survival after discharge. Details of the survivors were sent to the Registrar General for Scotland, who issued copies of death certificates for the patients who had died between discharge and 1 January 1989. RESULTS: Of 497 patients, 119 (24%) died in the intensive therapy unit and 120 (24%) after discharge, leaving 258 (52%) who were still alive at two years. The median (APACHE II) score was 13 and about half of the patients were aged 55 years or more. A wide range of critical illnesses, except neurosurgical emergencies, were treated. Survival analysis showed that only 41 (34%) of 122 patients with an APACHE II score of greater than or equal to 20 were alive at one year (95% confidence interval 25 to 42) compared with 124 (80%) of 155 patients with a score of less than 10 (73 to 87). Of the 144 patients aged 65 or more, only 68 (47%) survived to one year (39 to 55) but 90 (83%) of the 109 patients aged between 18 and 34 survived a similar period (76 to 71). Mortality was also related to diagnostic category; 71% of trauma victims survived to one year compared with only 41% of those admitted with gastrointestinal pathology. Univariate analysis of the results showed that age, severity of illness, and diagnosis were all predictors of long term survival. Multivariate analysis, however, showed that only age and severity of illness were independent prognostic factors. CONCLUSIONS: Long term survival of patients treated in an intensive therapy unit is related to severity of illness and to age. The outcome from critical illness in the elderly population is poor.
Long-term effects of dietary fructose on carbohydrate metabolism in non-insulin-dependent diabetes mellitus.
The effect of dietary fructose on glycemic control in subjects with diabetes mellitus is controversial. Therefore our aim was to conduct a long-term study to examine the effects of dietary fructose on glucose tolerance and insulin sensitivity and to delineate the mechanisms for the effects observed. Six subjects with non-insulin-dependent diabetes mellitus (NIDDM) who were being treated by diet alone consumed 13% of their calories as fructose incorporated into mixed meals in place of sucrose for 3 months as inpatients on a metabolic ward. The following parameters were measured: (1) weekly fasting plasma-glucose concentrations, (2) postprandial serum glucose and insulin levels after four sugar tolerance tests, (3) basal hepatic glucose production, and (4) hepatic and whole-body insulin sensitivity determined during a hyperinsulinemic, euglycemic clamp. When modest amounts of fructose were substituted for sucrose in the diet for 3 months, basal hepatic glucose output remained unchanged (12.84 +/- 1.83 nmol/kg/min v 12.51 +/- 2.00 nmol/kg/min) as did hepatic insulin sensitivity (92% +/- 4% v 93% +/- 4% suppression) and peripheral glucose disposal (22.52 +/- 4.56 nmol/kg/min v 25.80 +/- 9.45 nmol/kg/min) to a 860 pmol/m2/min insulin infusion at euglycemia (4.8 mmol/L). Fructose feeding also did not alter fasting plasma-glucose concentrations or postprandial plasma glucose and insulin responses to oral glucose or fructose loads or to mixed meals containing either sucrose or fructose. In conclusion, substitution of physiologic amounts of sucrose by fructose for prolonged periods is unlikely to have adverse effects on glucose metabolism in diabetic subjects who are being treated with diet alone.
Cholesterol lowering effect of jackbean (Canavalia ensiformis) seed protein.
1. Feeding jackbean (Canavalia ensiformis) protein to hypercholesterolemic rats considerably lowered cholesterol levels in the experimental animals than when the animals were fed casein (control) diets. 2. The cholesterol levels in various components of test animals fed the Canavalia diet ranged from 53.3 +/- 1.7 to 74.8 +/- 3.4 mg/g (plasma); from 11.1 +/- 7.4 to 23.3 +/- 5.4 mg/g (liver); from 7.1 +/- 0.7 to 9.3 +/- 1.7 mg/g (kidney) and 1.9 +/- 0.3 to 3.2 +/- 0.6 mg/g (heart). 3. Total lipid levels estimated for the animals on the test diets ranged from 80.0 +/- 2.4 to 130.1 +/- 9.1 mg/g (plasma); from 19.1 +/- 3.4 to 28.5 +/- 1.1 mg/g (liver); from 17.0 +/- 4.1 to 23.0 +/- 6.0 mg/g (kidney) and from 13.2 +/- 4.0 to 18.0 +/- 2.5 mg/g (heart). 4. Total protein levels in plasma of experimental animals were not significantly different (P less than 0.05) after feeding the control or test diets.
Use of a variable tracer infusion method to determine glucose turnover in humans.
The single-compartment pool fraction model, when used with the hyperinsulinemic glucose clamp technique to measure rates of glucose turnover, sometimes underestimates true rates of glucose appearance (Ra) resulting in negative values for hepatic glucose output (HGO). We focused our attention on isotope discrimination and model error as possible explanations for this underestimation. We found no difference in [3-3H] glucose specific activity in samples obtained simultaneously from the femoral artery and vein (2,400 +/- 455 vs. 2,454 +/- 522 dpm/mg) in 6 men during a hyperinsulinemic euglycemic clamp study where insulin was infused at 40 mU.m-2.min-1 for 3 h; therefore, isotope discrimination did not occur. We compared the ability of a constant (0.6 microCi/min) vs. variable tracer infusion method (tracer added to the glucose infusate) to measure non-steady-state Ra during hyperinsulinemic clamp studies. Plasma specific activity fell during the constant tracer infusion studies but did not change from base line during the variable tracer infusion studies. By maintaining a constant plasma specific activity the variable tracer infusion method eliminates uncertainty about changes in glucose pool size. This overcame modeling error and more accurately measures non-steady-state Ra (P less than 0.001 by analysis of variance vs. constant infusion method). In conclusion, underestimation of Ra determined isotopically during hyperinsulinemic clamp studies is largely due to modeling error that can be overcome by use of the variable tracer infusion method. This method allows more accurate determination of Ra and HGO under non-steady-state conditions.
Intracellular glucose oxidation and glycogen synthase activity are reduced in non-insulin-dependent (type II) diabetes independent of impaired glucose uptake.
To examine whether reduced rates of oxidative (Gox) and non-oxidative (Nox) glucose metabolism in non-insulin-dependent diabetes mellitus (NIDDM) are due to reduced glucose uptake, intrinsic defects in intracellular glucose metabolism or increased fat oxidation (Fox), indirect calorimetry was performed at similar glucose uptake rates in eight nonobese NIDDM and eight comparable nondiabetic subjects. Three glucose clamp studies were performed: one in the nondiabetic and two in the NIDDM subjects. In the nondiabetic subjects, glucose uptake was increased to 7.62 +/- 0.62 mg/kg of fat-free mass (FFM) per min by increasing serum insulin to 309 pmol/liter at a glucose concentration of 5.1 mmol/liter. By raising the concentration of either serum glucose or insulin fourfold in the NIDDM subjects, glucose uptake was matched to nondiabetic subjects (8.62 +/- 0.49 and 8.59 +/- 0.51 mg/kg FFM per min, respectively, P = NS). Skeletal muscle glycogen synthase activity and plasma lactate levels were measured to characterize Nox. When glucose uptake was matched to nondiabetics by hyperglycemia or hyperinsulinemia, Gox was reduced by 26-28% in NIDDM (P less than 0.025) whereas Fox was similar. Nox was greater in NIDDM (P less than 0.01) and was accompanied by increases in circulating lactate levels. Glycogen synthase activity was reduced by 41% (P less than 0.025) when glucose uptake was matched by hyperglycemia. Glycogen synthase activity was normalized in NIDDM, however, when glucose uptake was matched by hyperinsulinemia. Therefore, a defect in Gox exists in nonobese NIDDM subjects which cannot be overcome by increasing glucose uptake or insulin. Since both glucose uptake and Fox were similar in the two subject groups these factors were not responsible for reduced Gox. Increased Nox in NIDDM is primarily into lactate. Reduced glycogen synthase activity in NIDDM is independent of glucose uptake but can be overcome by increasing the insulin concentration.
Effects of weight loss and reduced hyperglycemia on the kinetics of insulin secretion in obese non-insulin dependent diabetes mellitus.
Impairment in pancreatic production of insulin, a cardinal feature of noninsulin dependent diabetes mellitus (NIDDM), was quantified and the kinetics of insulin secretion characterized in six obese individuals with NIDDM before and after weight loss (18.0 +/- 3.0 kg, mean +/- SEM) using a validated mathematical model that employs C-peptide as a marker of the in vivo rate of insulin secretion. The metabolic clearance of C-peptide, assessed by decay analysis after bolus injection of biosynthetic human C-peptide, was not changed by weight loss (0.143 +/- 0.009 L/min.m2 vs. 0.137 +/- 0.010 L/min.m2). Kinetic parameters from each individual's decay curve before and after weight loss were used to derive accurate rates of secretion during the basal (postabsorptive) state, an oral glucose tolerance test and two hyperglycemic clamps. Basal rates of insulin secretion declined 20 +/- 5 pmol/min.m2 (96 +/- 15 to 76 +/- 15 pmol/min.m2, P less than 0.05) concomitant with decreases of 6.9 +/- 0.9 mmol/L in fasting serum glucose (13.7 +/- 1.0 to 6.8 +/- 0.7 mmol/L, P less than 0.05), 60 +/- 14 pmol/L in serum insulin (134 +/- 30 to 74 +/- 15 pmol/L, P less than 0.05), and 0.15 +/- 0.03 pmol/ml in plasma C-peptide (0.67 +/- 0.11 to 0.52 +/- 0.08 pmol/ml, P less than 0.05) concentrations. As expected, weight loss resulted in improved glucose tolerance as measured by the glycemic profiles during the oral glucose tolerance test (P less than 0.05 analysis of variance). The insulin secretory response before weight loss showed a markedly reduced ability to respond appropriately to an increase in the ambient serum glucose. After weight loss, the pancreatic response was more dynamic (P less than 0.05, analysis of variance) and parralleled the moment-to-moment changes in glycemia. Insulin production above basal doubled (11.2 +/- 3.2 to 24.5 +/- 5.8 nmol/6h.m2, P less than 0.05) and peak rates of insulin secretion above basal tripled (55 +/- 16 to 157 +/- 32 pmol/min/m2, P less than 0.05). To assess the beta-cell response to glucose per se and the changes associated with weight reduction, two hyperglycemic clamps were performed at steady state glucose levels in the range characteristic of individuals with severe NIDDM. At a fixed glycemia of 20 mmol/L, average rates of insulin secretion increased almost 2-fold with treatment (161 +/- 41 to 277 +/- 60 pmol/min.m2, P less than 0.05). At an increment of 6 mmol/L glucose above prevailing fasting glucose levels, the average rate of insulin secretion increased 53% (120 +/- 21 to 183 +/- 39 pmol/min.m2, P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)
Kinetics of insulin-mediated and non-insulin-mediated glucose uptake in humans.
The kinetics of insulin-mediated glucose uptake (IMGU) and non-insulin-mediated glucose uptake (NIMGU) in humans have not been well defined. We used the glucose-clamp technique to measure rates of whole-body and leg muscle glucose uptake in six healthy lean men during hyperinsulinemia (approximately 460 pM) to study IMGU and during somatostatin-induced insulinopenia to study NIMGU at four glucose levels (4.5, 9, 12, and 21 mM). To measure leg glucose uptake, the femoral artery and vein were catheterized, and blood flow was measured by thermodilution (leg glucose uptake = arteriovenous glucose difference [A-VG] x blood flow). With this approach, we found that, during hyperinsulinemia, both whole-body and leg glucose uptake increased in a curvilinear fashion at every glucose level, the highest glucose uptake values obtained being 139 +/- 17 mumol.kg-1.min-1 and 3656 +/- 931 mumol.min-1.leg-1, respectively. Leg blood flow increased twofold from 6.0 +/- 1.7 to 11.7 +/- 3.1 dl/min (P less than 0.01) over the range of glucose and was correlated with whole-body glucose uptake (r = 0.55, P less than 0.005). Leg muscle glucose extraction, independent of changes in blood flow, which is reflected by the A-VG, saturated over the range of glucose (1.28 +/- 0.12, 2.22 +/- 0.30, 2.92 +/- 0.42, 3.02 +/- 0.41 mM, NS between last 2 values) with a half-maximal effective glucose concentration (EG50) of 5.3 +/- 0.4 mM.(ABSTRACT TRUNCATED AT 250 WORDS)
Kinetics of in vivo muscle insulin-mediated glucose uptake in human obesity.
The kinetics of in vivo insulin-mediated glucose uptake in human obesity have not been previously studied. To examine this, we used the glucose-clamp technique to measure whole-body and leg muscle glucose uptake in seven lean and six obese men during hyperinsulinemia (approximately 2000 pM) at four glucose levels (approximately 4.5, approximately 8.3, approximately 13.5, and approximately 23.5 mM). To measure leg glucose uptake, the femoral artery and vein were catheterized, and blood flow was measured by thermodilution (leg glucose uptake = arteriovenous glucose difference x blood flow). With this approach, we found that rates of whole-body and leg glucose uptake were significantly lower in obese than in lean subjects at each glucose plateau. Leg blood flow rates increased from 4.3 +/- 0.4 to 6.5 +/- 0.8 dl/min over the range of glucose in lean subjects (P less than 0.05) but remained unchanged in obese subjects. The apparent maximal capacity (Vmax), based on whole-body and leg glucose uptake, was reduced in obese compared with lean subjects, but the apparent Km was similar in the lean and obese subjects (6-9 mM, NS). To assess the affinity of muscle for glucose extraction independent of changes in muscle plasma flow, we determined the mean half-maximal effective glucose concentration (EG50) and found it was similar in the lean and obese subjects (6.0 +/- 0.3 vs. 6.0 +/- 0.8 mM, NS). We conclude that 1) the kinetics of in vivo insulin-mediated glucose uptake in skeletal muscle in human obesity are characterized by reduced Vmax but normal Km; 2) the EG50 for insulin-mediated glucose extraction in skeletal muscle was 6 mM in both lean and obese subjects, consistent with a Km characteristic of the glucose-transport system; 3) obese subjects were unable to generate increases in blood flow in response to hyperglycemia under hyperinsulinemic conditions, and this contributed significantly to lower rates of leg and whole-body glucose uptake.