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Biomedical subjects

J M Amatruda

Publications and source records attributed to J M Amatruda.

At least 19 recordsLinked to original sources
PubMed1998

13C/31P NMR studies on the mechanism of insulin resistance in obesity.

The mechanism of insulin resistance in obesity was examined in ten obese (BMI 33 +/- 1 kg/m2) and nine lean (BMI 22 +/- 1 kg/m2) Caucasian women during a hyperglycemic-hyperinsulinemic clamp using 13C and 31P nuclear magnetic resonance (NMR) spectroscopy to measure rates of muscle glycogen synthesis and intramuscular glucose-6-phosphate (G-6-P) concentrations. Under similar steady-state plasma concentrations of glucose (approximately 11 mmol/l) and insulin (approximately 340 pmol/l), rates of muscle glycogen synthesis were reduced approximately 70% in the obese subjects (52 +/- 8 micromol/[l muscle-min]) as compared with the rates in the lean subjects (176 +/- 22 micromol/[l muscle-min]; P < 0.0001). Basal concentrations of intramuscular G-6-P were similar in the obese and lean subjects; but during the clamp, G-6-P failed to increase in the obese group (deltaG-6-P obese 0.044 +/- 0.011 vs. lean 0.117 +/- 0.011 mmol/l muscle; P < 0.001), reflecting decreased muscle glucose transport and/or phosphorylation activity. We conclude that insulin resistance in obesity can be mostly attributed to impairment of insulin-stimulated muscle glycogen synthesis due to a defect in glucose transport and/or phosphorylation activity.

Adult↗
PubMed1995

The effects of weight reduction to ideal body weight on body fat distribution.

Obesity is a well-known health risk factor. Several studies have demonstrated that upper-body fat distribution plays a major role in the association between increased adiposity and metabolic disorders. The present study was undertaken to evaluate changes in intraabdominal and subcutaneous fat areas in obese subjects undergoing a weight reduction to their ideal body weight (IBW), as defined by a body mass index (BMI) no greater than 21 or body fat less than 30%, and compare the fat distribution at IBW with that of never-obese control subjects. We studied 33 obese women (151% +/- 1% of IBW; BMI, 31.6 +/- 2.5 [mean +/- SE]) before and after weight loss and a control group of 16 never-obese women (101.0% +/- 1.0% of IBW; BMI, 21.2 +/- 1.1). Eighteen obese women successfully achieved and stabilized at IBW for at least 2 months. Nonsuccessful obese subjects were significantly younger than reduced-weight subjects, but other physical characteristics were similar. In obese, reduced-obese, and never-obese groups, weight was 85 +/- 2.0, 62 +/- 1, and 58 +/- 1 kg; percent body fat was 41% +/- 1%, 24% +/- 2%, and 23% +/- 1%; intraabdominal fat area was 82 +/- 5, 28 +/- 3, and 25 +/- 4 cm2; waist subcutaneous fat area was 275 +/- 15, 120 +/- 9, and 81 +/- 7 cm2; hip subcutaneous fat area was 416 +/- 17, 204 +/- 10, and 195 +/- 7 cm2; and waist to hip ratio (WHR) was 0.84 +/- 0.02, 0.77 +/- 0.01, and 0.73 +/- 0.01, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1995

Overexpression of Glut4 protein in muscle increases basal and insulin-stimulated whole body glucose disposal in conscious mice.

The effect of increased Glut4 protein expression in muscle and fat on the whole body glucose metabolism has been evaluated by the euglycemic hyperinsulinemic clamp technique in conscious mice. Fed and fasting plasma glucose concentrations were 172 +/- 7 and 78 +/- 7 mg/dl, respectively, in transgenic mice, and were significantly lower than that of nontransgenic littermates (208 +/- 5 mg/dl in fed; 102 +/- 5 mg/dl in fasting state). Plasma lactate concentrations were higher in transgenic mice, (6.5 +/- 0.7 mM in the fed and 5.8 +/- 1.0 mM in fasting state) compared with that of non-transgenic littermates (4.7 +/- 0.3 mM in the fed and 4.2 +/- 0.5 mM in fasting state). In the fed state, the rate of whole body glucose disposal was 70% higher in transgenic mice in the basal state, 81 and 54% higher during submaximal and maximal insulin stimulation. In the fasting state, insulin-stimulated whole body glucose disposal was also higher in the transgenic mice. Hepatic glucose production after an overnight fast was 24.8 +/- 0.7 mg/kg per min in transgenic mice, and 25.4 +/- 2.7 mg/kg per min in nontransgenic mice. Our data demonstrate that overexpression of Glut4 protein in muscle increases basal as well as insulin-stimulated whole body glucose disposal. These results suggest that skeletal muscle glucose transport is rate-limiting for whole body glucose disposal and that the Glut4 protein is a potential target for pharmacological or genetic manipulation for treatment of patients with non-insulin-dependent diabetes mellitus.

Animals↗
PubMed1993

Total and resting energy expenditure in obese women reduced to ideal body weight.

Obesity could be due to excess energy intake or decreased energy expenditure (EE). To evaluate this, we studied 18 obese females (148 +/- 8% of ideal body weight [IBW], mean +/- SD) before and after achieving and stabilizing at IBW for at least 2 mo and a control group of 14 never obese females (< 110% of IBW or < 30% fat). In the obese, reduced obese, and never obese groups, the percent of body fat was 41 +/- 4%, 27 +/- 4%, and 25 +/- 3%; total energy expenditure (TEE) was 2704 +/- 449, 2473 +/- 495, and 2259 +/- 192 kcal/24 h; while resting metabolic rate was 1496 +/- 169, 1317 +/- 159, and 1341 +/- 103 kcal/24 h, respectively. 15 obese subjects who withdrew from the study had a mean initial body composition and EE similar to the subjects who were successful in achieving IBW. In 10 subjects followed for at least one year after stabilizing at IBW there was no significant relationship between the deviation from predicted TEE at IBW and weight regain. These studies indicate that, in a genetically heterogeneous female population, neither the propensity to become obese nor to maintain the obese state are due to an inherent metabolic abnormality characterized by a low EE.

Adult↗
PubMed1992

Increased protein turnover in obese women.

Some previous studies have indicated that rates of proteolysis and protein synthesis are greater in obese than in lean subjects, whereas others have not supported this finding. In the present study, we have measured postabsorptive protein turnover in a large group (n = 24) of obese women to establish more conclusively whether obese women have higher rates of protein turnover than lean women (n = 12), and to determine whether obese subjects with the greatest abdominal fat accumulation or those with the most severe insulin resistance (as determined by oral glucose tolerance testing) have the highest rates of protein turnover. Leucine appearance rate (Ra) was used as an index of whole-body proteolysis, and the fraction of Ra not oxidized was used as an index of whole-body protein synthesis. Leu Ra, oxidation, and incorporation into protein after an overnight fast were approximately 25% greater in obese than in lean women, and were approximately 10% to 15% greater after dividing by lean body mass (LBM) or adjusting for LBM by analysis of covariance. Among obese women, the degree of obesity (over the range of 30% to 47% fat) was not a significant determinant of protein turnover, nor were degree of insulin resistance, visceral fat accumulation (determined by magnetic resonance imaging [MRI]), or subcutaneous abdominal fat accumulation (also determined by MRI). However, the women with the highest rates of protein turnover also had higher waist to hip circumference ratios (WHR). We conclude that even moderate obesity is associated with increased protein turnover, and that this effect is not completely explained by the higher LBM in obese subjects.

Abdomen↗
PubMed1992

Energy expenditure under free-living conditions in normal-weight and overweight women.

Total energy expenditure under free-living conditions of 12 normal-weight and 26 overweight women was determined with the 2H2(18)O method. Overweight women tended to expend more energy (mean +/- SD, 11.20 +/- 1.79 MJ/d) than normal-weight women (9.46 +/- 0.87 MJ/d, P less than 0.005). Approximately half of this effect was explained by an increase in basal metabolic rate (BMR) in the overweight group compared with the normal-weight group (6.47 +/- 0.74 vs 5.68 +/- 0.39 MJ/d, respectively, P less than 0.005) and the other half by an increase in above-basal energy expenditure (4.73 +/- 1.49 vs 3.78 +/- 0.94 MJ/d, P less than 0.05). Total energy expenditure was approximately 1.7 times the BMR in both groups. After adjusting energy expenditure for weight or lean body mass by analysis of covariance, there was no significant difference between normal-weight and overweight groups. We conclude that most overweight subjects must consume more energy than lean subjects to maintain their excess weight, although some could maintain their obesity without eating more than lean subjects.

Adult↗
PubMed1991

Insulin inhibits apolipoprotein B secretion in isolated human hepatocytes.

The effect of insulin on apolipoprotein (apo) B secretion was investigated in human hepatocytes. Freshly isolated hepatocytes, prepared by collagenase dispersion of liver specimens, were incubated in serum-free media in the absence and presence of 100 nmol/L insulin for 2 hours. The media was then assayed for apo B content by radioimmunoassay. In hepatocytes incubated without insulin, the secretion of apo B (relative to human low-density lipoprotein [LDL]) was 125 +/- 37 ng/10(6) cells/2 hours. In the presence of insulin, apo B secretion was reduced to 83 +/- 29 ng/10(6) cells/2 hours (34% inhibition, P less than .05). These results using human hepatocytes are consistent with previous data from our laboratory describing insulin-dependent inhibition of apo B secretion in primary cultures of rat hepatocytes and studies by others employing the human-derived hepatoma cell line, Hep G2. We conclude that human hepatic apo B secretion is under insulin control. The role of more chronic insulin exposure requires further investigation.

Apolipoproteins B↗
PubMed1990

Insulin regulates apolipoprotein B turnover and phosphorylation in rat hepatocytes.

Our laboratory has previously shown that insulin inhibits the secretion of newly-synthesized and immunoreactive apo B from rat hepatocytes. We have also shown that apo B is secreted as a phosphoprotein and that phosphorylation is increased in hypoinsulinemic nonketotic diabetes. The present studies were conducted to determine whether the ability of insulin to inhibit apo B secretion is related to alterations in apo B turnover and whether insulin itself affects apo B phosphorylation. Pulse-chase studies with [35S]methionine in primary cultures of hepatocytes from normal rats in the absence and presence of insulin show that the secretion of apo B100 and apo B48 are inhibited by insulin and that this inhibition may be due in part to enhanced intracellular degradation. In addition, there is a second intracellular apo B48 pool which is not insulin regulated or degraded. In experiments in which hepatocytes were incubated with [32P]orthophosphate, insulin decreased 32P incorporation into apo B100 (42%) with only small effects on apo B48 (11%). The small insulin effect on apo B48 may relate to an insulin-insensitive apo B48 intracellular pool. These studies show that insulin can affect the intracellular turnover, secretion, degradation, and phosphorylation of apo B and emphasize the differential regulation of apo B100 and apo B48 with regard to these parameters in rat liver.

Animals↗
PubMed1989

Hormone and substrate regulation of glycogen accumulation in primary cultures of rat hepatocytes.

Hormonal and substrate regulation of hepatic glycogen accumulation was evaluated in primary cultures of hepatocytes prepared from 1-day-fasted rats. Hepatocytes were cultured in media containing 5 mM-glucose and 10 mM-lactate and then exposed to 100 nM-dexamethasone for 4 h before an increase in glucose concentration and the addition of insulin. When this protocol was used to mimic the post-prandial state in vivo, net glycogen accumulation (over 2 h) and insulin (10 nM) effects were linear at physiological (5-10 mM) and supraphysiological (20-30 mM) glucose concentrations. To define the role of substrates in glycogen accumulation, hepatocytes were incubated in a buffered salt solution containing 10 mM-glucose and either 10 mM-lactate or 5 mM-glutamine, or both. In the absence of hormones, net glycogen accumulation was increased by 59%, 83%, and 127% by the addition of lactate, glutamine, and lactate plus glutamine respectively, compared with incubations with glucose alone, and 6-fold in the presence of substrates, insulin and dexamethasone. Labelling with [3-3H]glucose and [U-14C]glucose showed that in the absence of hormones approx. 50% of glycogen formation came from glucose via the direct pathway and the remainder from glucose via the indirect pathway or from non-glucose precursors, or both. Insulin-dependent enhancement of glycogen formation is through stimulation of both the direct and indirect pathways, and dexamethasone-dependent stimulation occurs through stimulation of both these pathways of glycogen formation from glucose as well as from non-glucose precursors. Lactate serves as a gluconeogenic C3 precursor for the observed enhanced glycogen formation, whereas glutamine-dependent enhancement of glycogen accumulation occurs primarily through a stimulation of the direct and indirect pathways of glycogen formation from glucose.

Animals↗
PubMed1989

Postreceptor regulation of insulin action in primary cultures of rat hepatocytes by oral hypoglycemic agents: effects of linogliride and chlorpropamide.

We have previously demonstrated the ability of the sulfonylurea tolazamide to potentiate insulin action in primary cultures of hepatocytes prepared from normal and streptozotocin-diabetic rats. To determine whether the pirogliride derivative linogliride, a non-sulfonylurea orally effective hypoglycemic agent, can potentiate insulin action, we evaluated the ability of linogliride to affect insulin-stimulated lipogenesis in primary cultures of hepatocytes prepared from normal rats. In addition, we also evaluated the ability of the sulfonylurea chlorpropamide to affect insulin-stimulated lipogenesis in the same in vitro system. The exposure of hepatocytes for 18 h to either linogliride (100 ug/ml) or chlorpropamide (175 ug/ml) resulted in dose-dependent (0.1 to 100 nM insulin) increases in insulin-stimulated lipogenesis, although the effects of chlorpropamide are approximately two times those of linogliride. This increase in insulin responsiveness was not associated with any change in insulin sensitivity (ED50) or insulin binding. The results provide evidence for an extra-pancreatic effect of linogliride and chlorpropamide in the liver and indicate that these structurally unrelated oral hypoglycemic agents enhance insulin responsiveness through postbinding mechanisms.

Animals↗
PubMed1988

Secretion of high and low molecular weight phosphorylated apolipoprotein B by hepatocytes from control and diabetic rats. Phosphorylation of APO BH and APO BL.

Apolipoprotein B (apo B) phosphorylation was examined in primary cultures of hepatocytes from control and nonketotic streptozotocin diabetic rats. Following a 5-h incubation with ortho[32P]phosphate, media lipoproteins (d less than 1.063 g/ml) were isolated, and delipidated apolipoproteins were separated by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis (SDS-PAGGE), and gels were heat fixed. Autoradiographic bands corresponding to high (apo BH) and low molecular weight apo B (apo BL) were observed in media lipoproteins isolated from control rats, and these bands were more prominent in media lipoproteins isolated from diabetic rats. Apo B-specific activity was estimated from aqueous alcohol-precipitated radioactivity and apo B monoclonal immunoassay of isolated media lipoproteins. In lipoproteins secreted by hepatocytes of diabetic rats, the calculated apo B specific activity was between 18- and 31-fold greater than that secreted by hepatocytes of control rats, consistent with the SDS-PAGGE gel data. The increase in secretory 32P-labeled apo B from hepatocytes of diabetic rats was due, at least in part, to an increase in labeled phospho-tyrosine as determined by phosphoamino acid analysis. These data demonstrate that apo BH may be secreted as a phosphorylated protein and that apo B phosphorylation occurs on tyrosine as well as serine residues.

Animals↗
PubMed1988

Role of sialic acid in insulin action and the insulin resistance of diabetes mellitus.

Adipocytes treated with neuraminidase show markedly reduced responsiveness to insulin without any alteration in insulin binding. In addition, several studies have separately demonstrated both insulin resistance and decreases in membrane sialic acid content and associated biosynthetic enzymes in diabetes mellitus. In the present study, we investigated the role that sialic acid residues may play in insulin action and in the hepatic insulin resistance associated with nonketotic diabetes. Primary cultures of hepatocytes from normal rats treated with neuraminidase demonstrated a dose-dependent decrease in insulin-stimulated lipogenesis. At a concentration of neuraminidase that decreases insulin action by 50%, 23% of total cellular sialic acid content was released. Neuraminidase-releasable sialic acid was significantly decreased in hepatocytes from diabetic rats and this was associated with significant insulin resistance. Treatment of hepatocytes from diabetic rats with cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA) enhanced insulin responsiveness 39%. The enhanced insulin responsiveness induced by CMP-NANA was blocked by cytidine 5'-monophosphate (CMP) suggesting that the CMP-NANA effect was catalyzed by a cell surface sialyltransferase. CMP reduced neuraminidase-releasable [14C]sialic acid incorporation into hepatocytes by 43%. The data demonstrate a role for cell surface sialic acid residues in hepatic insulin action and support a role for decreased cell surface sialic acid residues in the insulin resistance of diabetes mellitus.

Animals↗
PubMed1988

Effects of nonketotic streptozotocin diabetes on apolipoprotein B synthesis and secretion by primary cultures of rat hepatocytes.

The effects of hypoinsulinemic nonketotic streptozotocin diabetes on hepatic apo B synthesis and secretion was studied in primary cultures of rat hepatocytes. Diabetic rats were characterized by their significantly elevated serum glucose, apo B, and triglyceride levels, while serum insulin levels were less than a third of normal. Serum transminase activities of diabetic rats were significantly elevated when compared with control rats, which was attributed to an increase in liver transaminase activity in diabetic rats. The pattern of enzyme activities of hepatocytes reflected that observed in livers of donor rats and the pattern was retained by primary cultures of hepatocytes over the culture period. Hepatocytes from diabetic rats secreted only one third of the apo B secreted by hepatocytes from control rats, which was determined by monoclonal immunoassay of rat total apo B. Decreases in secretion were confirmed by measurement of secretory [35S]methionine-labeled lipoprotein apo B radioactivity. The decreased apo B content of media of hepatocytes from diabetic rats was not due to increased apo B catabolism since hepatocytes from diabetic rats were shown to degrade less lipoprotein-apo B than hepatocytes from normal rats in control experiments. In addition, the apo B content of detergent-solubilized hepatocytes from diabetic rats was significantly less than that of hepatocytes from control rats. These results suggest that insulin is necessary for normal hepatic apo B synthesis and secretion and that the hyperlipidemia associated with hypoinsulinemia in vivo is primarily of intestinal origin.

Animals↗
PubMed1988

The accuracy of blood glucose testing by children.

While studies have evaluated the accuracy of adult patients and health personnel in reading various glucose oxidase impregnated strips to estimate blood glucose, there are no studies exclusively evaluating the accuracy of children with diabetes reading their own strips as compared to a staff member, and meter to meter variability in reading these strips. We evaluated the accuracy of reading chemstrip bG by children at a summer camp. The children's visual readings of their own strips were compared to the visual reading of a single staff member. A total of 356 Chemstrip bG's were visually read by diabetic children and a single trained staff member at a summer camp for diabetics. The strips were then analyzed by two Accu-Chek bG meters. Intermachine variability was found to be negligible over the entire bG range. For the purposes of this study, we define accurate visual readings as those within +/- 15 percent of the meter reading of a given strip. At low bG values (40-79 mg/dl), accuracy by children and staff is low, with underestimating occurring in 39 percent of staff readings and 57 percent of children's readings. At intermediate bG values (120-239 mg/dl) readings are more accurate, especially when read by the staff, with misreadings occurring in only 16-19 percent of the strips. At high bG values (240-399 mg/dl), accuracy by children is decreased, with underestimation 500 percent more often than staff. We conclude that children are less accurate at reading Chemstrip bG than a trained staff member (51% versus 33% misreading), especially at the upper and lower ranges of bG values when visual readings are least accurate, and the need for therapeutic intervention is the greatest.

Adolescent↗
PubMed1988

Insulin-mimetic effects of vanadate in primary cultures of rat hepatocytes.

To evaluate possible mechanisms by which insulin inhibits hepatic apolipoprotein B (apoB) secretion, we incubated primary cultures of rat hepatocytes with sodium orthovanadate, a phosphotyrosine phosphatase inhibitor and insulin-mimetic agent. Vanadate (10 microM) and insulin (10 nM) inhibited the medium accumulation of apoB (secretion) by 21 and 37%, respectively, without increasing intracellular apoB. The effects of insulin and vanadate together were not additive. Both insulin and vanadate enhanced intracellular glycogen accumulation by 82 and 37%, respectively. Unlike insulin, vanadate, at a concentration that inhibited apoB secretion (10 microM), had no effect on intracellular lipogenesis, inhibited the secretion of newly synthesized hepatic proteins, and had a delayed onset and termination of action on inhibition of apoB secretion. At higher concentrations (40 and 80 microM), vanadate stimulated intracellular lipogenesis. In conclusion, our data indicate that vanadate mimics insulin action in hepatocytes with regard to the inhibition of medium accumulation of apoB. These data are consistent with the hypothesis that inhibition of apoB secretion may be secondary to an increase in phosphotyrosine content at its site of synthesis. The kinases responsible for this effect have not been identified. Several effects of vanadate, however, are different from those of insulin, suggesting a differential sensitivity to vanadate, a divergence of the signal transfer by insulin and vanadate at the insulin-receptor or postreceptor level, or both.

Acetates↗
PubMed1988

The safety and efficacy of a controlled low-energy ('very-low-calorie') diet in the treatment of non-insulin-dependent diabetes and obesity.

We evaluated the safety and efficacy of a highly supplemented controlled low-energy (1764 kJ [420 kcal]) diet in the treatment of non-insulin-dependent diabetes and obesity. Six obese, diabetic women ranging from 143% to 297% of ideal body weight were studied in a metabolic ward for 48 days. The subjects ingested a weight-maintenance diet during an eight-day control period followed by 40 days of an experimental diet containing 1764 kJ (420 kcal) of a mixture of protein (43% of energy intake), carbohydrates (51%), and fat (6%), supplemented with minerals, trace elements, and vitamins. The subjects were monitored for balances of nitrogen and minerals, as well as for the appearance of cardiac arrhythmias by 24-hour electrocardiographic recordings. Weight loss was rapid and sustained and averaged 10.1% +/- 0.8% over 40 days. Fasting plasma glucose levels declined from 16.2 +/- 1.9 mmol/L (293 +/- 36 mg/dL) to 6.9 +/- 0.8 mmol/L (126 +/- 16 mg/dL) by day 35. Similarly, hemoglobin A1c levels fell from 0.11 +/- 0.009 (11.2% +/- 0.9%) to 0.8 +/- 0.001 (8.2% +/- 1.1%). Urinary C-peptide levels declined from 62.2 +/- 15.6 nmol/48 h to 20.0 +/- 5.9 nmol/48 h by days 39 to 40 and paralleled the decline in plasma glucose values, the majority of which occurred in the first seven days. Concentrations of serum cholesterol and triglycerides decreased. Balances for nitrogen, potassium, and magnesium were negative at -1.7 g/24 h, -2.2 mEq/24 h, and -2.9 mg/dL, respectively. Blood pressure decreased without orthostasis. Resting metabolic rate fell a mean of 18% but remained within normal limits. Triiodothyronine levels also declined. Twenty-four-hour ambulatory electrocardiographic readings disclosed no significant bradyarrhythmia or tachyarrhythmia for any patient. These studies, based on a limited number of subjects, demonstrate that a highly supplemented controlled low-energy diet is a safe and efficacious treatment for diabetes and obesity, leading to significant decreases in weight, blood pressure, and levels of plasma glucose and plasma lipids. Such diets may be the optimal initial treatment of moderate to markedly obese patients with non-insulin-dependent diabetes.

Adult↗