Skeletal muscle glucose uptake, glycogen synthase activity and GLUT 4 content during hypoglycaemia in type 1 diabetic subjects.

In healthy subjects, hypoglycaemia induces a profound 80% reduction in skeletal muscle glucose uptake and a similar suppression of glycogen synthase activity. The aim of this study was to examine the efficacy of this counterregulatory mechanism in type 1 diabetic subjects, who are especially prone to hypoglycaemic incidents. Nine type 1 diabetic male subjects were examined twice; during 120 min of hyperinsulinaemic (1.5 mU x kg(-1) x min(-1)) euglycaemia followed by (i) 240 min of graded hypoglycaemia (glucose nadir 2.8 mM) or (ii) 240 min of euglycaemia. At 345-360 min a muscle biopsy was taken and indirect calorimetry was performed at 210-240 and 320-340 min. The sensitivity of glycogen synthase to glucose-6-P was reduced by hypoglycaemia, as shown by an increase in A0.5 for glucose-6-P (at 0.07 mmol/L) from 0.21+/-0.02 to 0.28+/-0.03 mM (p=0.06). Likewise, the fractional velocity for glycogen synthase was reduced by 25%; i.e. from 20.8+/-2.0 to 15.5+/-1.4% (p<0.05). Total glucose disposal was decreased during hypoglycaemia (5.3+/-0.6 vs. 8.3+/-0.7 mg x kg(-1) x min(-1) (euglycaemia), n = 9; p<0.05), primarily due to a reduction of non-oxidative glucose disposal (2.7+/-0.3 vs. 5.1+/-0.6 mg x kg(-1) x min(-1) (euglycaemia), n=7; p<0.05). Forearm arteriovenous glucose differences were decreased by 50% in the hypoglycaemic situation (0.7+/-0.1 vs. 1.4+/-0.3 mmol/L (320-340 min)), and counterregulatory hormonal responses seemed less conspicuous than described in healthy subjects. We conclude that hypoglycaemia induces decrements of forearm glucose uptake and glycogen synthase activity in type 1 diabetic subjects. The study indicates a decreased magnitude of these responses, but this remains to be confirmed.

Epinephrine stimulates human muscle lipoprotein lipase activity in vivo.

Lipoprotein lipase (LPL) is involved in lipoprotein metabolism and nutrient partitioning in both adipose tissue and skeletal muscle, and LPL activity is regulated by various hormones and the nutritional state. However, the action of catecholamines has not been thoroughly investigated in humans. Therefore, the effects of exogenous epinephrine on skeletal muscle LPL (SM-LPL) activity and whole-body lipid oxidation were studied. Muscle biopsies were obtained from eight healthy subjects before, during, and after epinephrine infusion. Somatostatin was infused to suppress endogenous insulin production and insulin was infused at a constant rate to maintain basal insulin levels throughout the study. After an equilibrium period (120 minutes), epinephrine (0.05 microg/kg/min) was infused for another 120 minutes. Epinephrine stimulated SM-LPL activity by 21.8%+/-6.8% above basal levels from 1.44+/-0.25 to 1.69+/-0.28 micromol free fatty acid (FFA)/h/g muscle (P<.02), increased plasma FFA 270% from 0.147 to 0.544 mmol/L (P<.05), and increased lipid oxidation 45% from 4.37 to 6.36 mg/kg/min (P<.05). The increase in SM-LPL activity was positively correlated with the increase in whole-body lipid oxidation (R=.75, P<.05). Finally, lipid oxidation and SM-LPL activity were negatively correlated with whole-body glucose oxidation. Overall, the results demonstrate that epinephrine is able to stimulate SM-LPL activity in humans, and thus may have opposite effects on adipose tissue and SM-LPL activity.

Effects of the somatostatin analog, octreotide, on glucose metabolism and insulin sensitivity in insulin-dependent diabetes mellitus.

To examine the effect of the somatostatin analog, octreotide, on insulin-mediated glucose uptake, seven insulin-dependent diabetic (IDDM) subjects were studied with and without 4 days of continuous subcutaneous octreotide administration (1 mg/kg/d). Insulin dosage was adjusted after frequent measurements of plasma glucose level. On the third day a hormonal and metabolic blood profile was obtained, and on the fourth day a euglycemic (5 mmol/L), hyperinsulinemic (1 mU/kg/min) clamp was performed in combination with calorimetry and a muscle biopsy. Mean plasma glucose levels on day 3 were similar (7.9 +/- 0.9 v 9.0 +/- 0.6 mmol/L). Growth hormone (GH) (0.39 +/- 0.10 v 0.78 +/- 0.23 mg/L, P < .05), insulin-like growth factor-1 (IGF-1) (127 +/- 17 v 157 +/- 21 mg/L, P < .05), and nonesterified fatty acids (NEFA) (239 +/- 25 v 405 +/- 44 mmol/L, P < .01) were lower following octreotide administration. Insulin requirements were reduced during octreotide administration, resulting in significantly lower insulin levels (27.3 +/- 2.7 v 39.9 +/- 9.9 mU/L, P < .5). During the clamp, glucose and insulin levels wer similar. Following octreotide, glucose disposal (7.33 +/- 0.49 v 6.08 +/- 0.55 mg/kg/min, P < .05) increased and hepatic glucose production (HGP) was more suppressed (-1.56 +/- 0.07 v -0.63 +/- 0.34 mg/kg/min, P < .05, 220 to 270 minutes). Oxidative glucose disposal (indirect calorimetry) was enhanced (3.09 +/- 0.24 v 2.70 +/- 0.37 mg/kg/min, P = .08), whereas glucose storage, as well as the fractional velocity for glycogen synthase activity, were unaltered during octreotide administration. Conversely, octreotide decreased lipid oxidation (0.12 +/- 0.1 v 0.41 +/- 0.15 mg/kg/min, P < .05). In conclusion, a low-dose octrotide infusion for 4 days to IDDM subjects leads to significantly increased insulin sensitivity.

Inhibition of muscle glycogen synthase activity and non-oxidative glucose disposal during hypoglycaemia in normal man.

The purpose of the present study was to evaluate the role of muscle glycogen synthase activity in the reduction of glucose uptake during hypoglycaemia. Six healthy young men were examined twice; during 120 min of hyperinsulinaemic (1.5 mU.kg-1. min-1) euglycaemia followed by: 1)240 min of graded hypoglycaemia (plasma glucose nadir 2.8 mmol/l) or 2) 240 min of euglycaemia. At 350-360 min a muscle biopsy was taken and indirect calorimetry was performed at 210-240 and 330-350 min. Hypoglycaemia was associated with markedly increased levels of adrenaline, growth hormone and glucagon and also with less hyperinsulinaemia. During hypoglycaemia the fractional velocity for glycogen synthase was markedly reduced; from 29.8 +/- 2.3 to 6.4 +/- 0.9%, p < 0.05. Total glucose disposal was decreased during hypoglycaemia (5.58 +/- 0.55 vs 11.01 +/- 0.75 mg.kg-1. min-1 (euglycaemia); p < 0.05); this was primarily due to a reduction of non-oxidative glucose disposal (2.43 +/- 0.41 vs 7.15 +/- 0.7 mg.kg-1 .min-1 (euglycaemia); p < 0.05), whereas oxidative glucose disposal was only suppressed to a minor degree. In conclusion hypoglycaemia virtually abolishes the effect of insulin on muscle glycogen synthase activity. This is in keeping with the finding of a marked reduction of non-oxidative glucose metabolism.

Long-term effects of fluoxetine on glycemic control in obese patients with non-insulin-dependent diabetes mellitus or glucose intolerance: influence on muscle glycogen synthase and insulin receptor kinase activity.

Fluoxetine (F) is a specific serotonin-reuptake inhibitor that has been shown to promote weight loss and improve glycemic control in obese diabetic patients. To study its long-term metabolic effect, 40 obese patients with non-insulin -dependent diabetes mellitus (NIDDM) or impaired glucose tolerance (IGT) were included in a 12-month, randomized, placebo controlled study. Patients were assigned to receive either 60 mg F or placebo (P) daily in conjunction with a 5.0-MJ/d diet (> 50% carbohydrate). Both groups showed a significant weight loss, with a nadir after 6 months without group differences (mean +/- SD: F, 10.1 +/- 10.0 kg; P, 9.4 +/- 11.5 kg). Fifteen patients from the F group and 14 from the P group completed the 12-month study without weight loss differences. Glycemic regulation improved along with the weight loss, but with a larger decline in plasma C-peptide and fasting glucose levels on the F group (P < .05). Total skeletal muscle glycogen synthase (GS) activity increased by 31% in the F group (P < .01) and by 17% in the P group (nonsignificant) after 6 months of treatment, but was still less than the activity in normal-weight controls (aged 28.0 +/- 6.3 years; body mass index, 23.5 +/- 2.2). After adjustment for fasting glucose, insulin, weight loss, and diabetic state, a positive effect of F remained on the total GS activity, which accounted for 27% of the variation (P < .05). The waist to hip ratio was reduced in P subjects as compared with F subjects (P < .05). Fat-free mass (FFM) tended to be more reduced in the F group as compared with P subjects (4.9 v 1.9 kg), although the difference did not reach statistical significance. In conclusion, F seems to improve insulin sensitivity beyond the effect mediated through weight loss by a possible effect on GS activity in skeletal muscle tissue.

Effect of needle biopsy from the vastus lateralis muscle on insulin-stimulated glucose metabolism in humans.

To examine the cellular mechanisms behind conditions characterized by insulin resistance, the clamp technique is often combined with muscle biopsies. To test whether the trauma of a needle biopsy from the vastus lateralis muscle per se may influence insulin-stimulated glucose uptake, eight healthy subjects underwent two randomly sequenced hyperinsulinemic (insulin infusion rate: 0.6 mU.kg-1.min-1 for 150 min) euglycemic clamps with an interval of 4-6 wk. In one study (study B) a muscle biopsy (approximately 250 mg, i.e., larger than normal standard) was taken in the basal state just before the clamp procedure, whereas the other was a control study (study C). Insulin-stimulated glucose uptake was significantly reduced in study B (5.36 +/- 0.96 mg.kg-1.min-1) compared with study C (6.06 +/- 0.68 mg.kg-1.min-1; P < 0.05). Nonoxidative glucose disposal (indirect calorimetry) was decreased (2.81 +/- 1.08 vs. 3.64 +/- 1.34 mg.kg-1.min-1; P < 0.05), whereas glucose oxidation was unaltered. Likewise, endogenous glucose output ([3-3H]glucose) was identically suppressed during hyperinsulinemia. Circulating levels of epinephrine, glucagon, and growth hormone did not differ significantly in studies B and C. In contrast, plasma norepinephrine, serum cortisol, and free fatty acid rose after biopsy (P < 0.05). In conclusion, performance of a muscle biopsy may diminish insulin sensitivity by affecting nonoxidative glucose metabolism. This should be considered when assessing whole body insulin sensitivity after a percutaneous needle muscle biopsy.

Effects of glipizide on glucose metabolism and muscle content of the insulin-regulatable glucose transporter (GLUT 4) and glycogen synthase activity during hyperglycaemia in type 2 diabetic patients.

To examine whether sulphonylureas influence hyperglycaemia-induced glucose disposal and suppression of hepatic glucose production (HGP) in type 2 diabetes mellitus, a 150-min hyperglycaemic (plasma glucose 14 mmol/l) clamp with concomitant somatostatin infusion was used in eight type 2 diabetic patients before and after 6 weeks of glipizide (GZ) therapy. During the clamp a small replacement dose of insulin was given (0.15 mU/kg per min). Isotopically determined glucose-induced glucose uptake was similar before and after GZ administration which led to improved glycaemic control (basal plasma glucose 12.2 +/- 1.3 vs 8.9 +/- 0.7 mmol/l; P < 0.01). Glucose-induced suppression of HGP was, however, more pronounced during GZ treatment (0.96 +/- 0.14 vs 1.44 +/- 0.20 mg/kg per min; P < 0.02). Following GZ treatment hyperglycaemia failed to stimulate glycogen synthase activity. Moreover, GZ resulted in a significant increase in the immunoreactive abundance of the insulin-regulatable glucose transport protein (GLUT 4) (P < 0.02). In conclusion, these results suggest that GZ therapy in type 2 diabetic patients enhances hepatic sensitivity to hyperglycaemia, while glucose-induced glucose uptake remains unaffected. In addition, GZ tends to normalize the activity of glycogen synthase and increases the content of GLUT 4 protein in skeletal muscle.

Insulin receptor function and glycogen synthase activity in human skeletal muscle. Physiology and pathophysiology.

Insulin stimulates glucose uptake and non-oxidative glucose metabolism (predominantly glycogen synthesis) in skeletal muscle. Among other things, insulin resistance is characterized by a subnormal insulin-stimulated glucose disposal, and it appears to be associated with an increased risk for development of non-insulin-dependent diabetes mellitus (NIDDM). The aim of the present investigation has been to elucidate the mechanism of action of insulin on non-oxidative glucose metabolism both during conditions of insulin resistance and during physiological modification of glucose metabolism. To do so, the effect of insulin was investigated both with respect to its initial activation of the insulin receptor kinase and the terminal step of the signal pathway, namely stimulation of the glycogen synthase. From needle biopsies of human skeletal muscle (vastus lateralis) cellular membranes were solubilized and the insulin receptors were partially purified by affinity chromatography using wheat germ agglutinin. Subsequently insulin binding and the insulin-stimulated tyrosine kinase activity were characterized. The insulin receptor kinase activity did not change during physiological modification of the glucose metabolism (exercise training, acute exercise, growth hormone exposure or experimental hyperglycemia). No specific abnormalities of the insulin receptor kinase activity were revealed in insulin-dependent diabetes (IDDM) or in common NIDDM. In addition, insulin receptor kinase activity did not change during dietary or sulphonylurea treatment of NIDDM. Glucose deposition as glycogen in muscle is regulated by glycogen synthase (GS), which during insulin stimulation undergoes dephosphorylation and becomes more active at physiological concentrations of glucose-6-phosphate. Recently, insulin was shown to stimulate a cascade of phosphorylation-dependent kinases which ultimately activate a glycogen-bound subunit of a phosphatase (G-subunit of phosphatase-1) which promotes dephosphorylation GS by the catalytic subunit. The quantity of the GS enzyme (GStot) in muscle may be reduced in the diabetes disease. However, it may increase during physical training of insulin-dependent diabetic patients. GStot is not altered during acute exposure to insulin, hyperglycemia or muscle contraction. The insulin stimulation of GS is reduced in insulin resistant NIDDM patients. However, once the hyperglycemia and the insulin resistance is ameliorated during treatment with diet or sulphonylurea drugs the activation of GS improves. Growth hormone-induced transient insulin resistance in non-diabetic subjects, is accompanied by a reduced insulin stimulation of GS. Experimentally induced hyperglycemia in normal subjects has no influence on GS activation by insulin. After an acute exercise bout the GS in muscle becomes activated. The mechanism of this post-exercise GS activation is still unknown.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of insulin receptor spliced variants and their functional correlates in muscle from patients with non-insulin-dependent diabetes mellitus.

Due to alternative splicing of exon 11 of the receptor gene, the human insulin receptor exists in two forms, that have distinct tissue-specific expression and are functionally different. Needle biopsies obtained from vastus lateralis muscle from 20 patients with noninsulin-dependent diabetes mellitus (NIDDM) and 20 normal control subjects were analyzed for the relative expression of insulin receptor mRNA variants in a novel assay using fluorescence-labeled primers and subsequent analysis on an automated DNA sequencer. In subgroups of patients and control subjects, insulin binding and tyrosine kinase activity were examined in wheat germ agglutinin-purified insulin receptors isolated from muscle biopsies. Moreover, insulin-stimulated glucose disposal was studied by means of the euglycemic hyperinsulinemic clamp technique. No difference in the relative expression of spliced variants of the insulin receptor mRNA was observed (control subjects, 71.4 +/- 1.3% insulin receptor mRNA with exon 11; NIDDM patients, 71.5 +/- 1.3% insulin receptor mRNA with exon 11). No significant interrelationships were demonstrated among the relative expression of insulin receptor mRNA variants, insulin binding, and tyrosine kinase activity toward the exogenous substrate poly(Glu-Tyr(4:1)). Furthermore, no significant relationship was demonstrated between the glucose disposal rate and the relative expression of insulin receptor splice variants. In conclusion, in skeletal muscle from both normal control subjects and NIDDM patients, the proportion of insulin receptor mRNA with exon 11 is about 70%. In addition, no significant correlations exist among insulin binding, insulin receptor tyrosine kinase activity, glucose disposal rate, and expression of alternative spliced insulin receptors in human skeletal muscle.

Abdominal obesity is associated with insulin resistance and reduced glycogen synthetase activity in skeletal muscle.

Insulin resistance is commonly associated with obesity. The present study was performed to investigate the relative importance of total fat mass versus localization of adipose tissue in insulin-stimulated glucose disposal (Rd) and skeletal muscle glycogen synthase (GS) activity in obese individuals. Twenty obese women with an average body mass index (BMI) of 37.8 +/- 1.3 kg/m2 and a waist to hip ratio (WHR) ranging from 0.78 to 1.02 were examined during basal conditions and following hyperinsulinemia (hyperinsulinemic euglycemic clamp). To accurately determine body composition, the following three methods were used: anthropometric measurements, dual-energy x-ray absorptiometry scanning (DEXA-scan), and bioelectric impedance measurements. In addition, indirect calorimetry and muscle biopsy were performed. Insulin-stimulated glucose Rd was negatively correlated with WHR (R = -.52, P < .025) whereas there were no correlations with BMI or percent fat (R = .16, NS and R = .16, NS, respectively). Furthermore, a negative correlation between WHR and insulin stimulation of GS activity in skeletal muscle was found (R = -.62, P < .005). In contrast, BMI and percent fat were not correlated with the insulin effect on GS activity in skeletal muscle (R = .34, NS and R = -.35, NS, respectively). The concentration of nonesterified fatty acids (NEFA) during hyperinsulinemia was strongly correlated with WHR and abdominal localization of adipose tissue (determined by DEXA-scan; R = .60, P < .005 and R = .60, P < .007, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo insulin action and muscle glycogen synthase activity in type 2 (non-insulin-dependent) diabetes mellitus: effects of diet treatment.

Insulin resistant glucose metabolism is a key element in the pathogenesis of Type 2 (non-insulin-dependent) diabetes mellitus. Insulin resistance may be of both primary (genetic) and secondary (metabolic) origin. Before and after diet-induced improvement of glycaemic control seven obese patients with newly-diagnosed Type 2 diabetes were studied with the euglycaemic clamp technique in combination with indirect calorimetry and forearm glucose balance. Muscle biopsies were obtained in the basal state and again after 3 h of hyperinsulinaemia (200 mU/l) for studies of insulin receptor and glycogen synthase activities. Similar studies were performed in seven matched control subjects. Insulin-stimulated glucose utilization improved from 110 +/- 11 to 183 +/- 23 mg.m-2.min-1 (p less than 0.03); control subjects: 219 +/- 23 mg.m-2.min-1 (p = NS, vs post-diet Type 2 diabetes). Non-oxidative glucose disposal increased from 74 +/- 17 to 138 +/- 19 mg.m-2.min-1 (p less than 0.03), control subjects: 159 +/- 22 mg.m-2.min-1 (p = NS, vs post-diet Type 2 diabetic patients). Forearm blood glucose uptake during hyperinsulinaemia increased from 1.58 +/- 0.54 to 3.35 +/- 0.23 mumol.l-1.min-1 (p less than 0.05), control subjects: 2.99 +/- 0.86 mumol.l-1.min-1 (p = NS, vs post-diet Type 2 diabetes). After diet therapy the increase in insulin sensitivity correlated with reductions in fasting plasma glucose levels (r = 0.97, p less than 0.001), reductions in serum fructosamine (r = 0.77, p less than 0.05), and weight loss (r = 0.78, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Basal- and insulin-stimulated substrate metabolism in patients with active acromegaly before and after adenomectomy.

Active acromegaly is characterized by inappropriate tissue growth, increased mortality, and perturbations of intermediary metabolism. It is, in general, not well described to which extent these disturbances are normalized after treatment of the disease. To further assess basal and insulin stimulated fuel metabolism in acromegaly six patients with monotropic GH excess were each studied approximately 1 month prior to and 2 months after successful selective pituitary adenomectomy and compared to a control population of seven subjects. The studies consisted of a 3-h basal postabsorptive period and a 2-h hyperinsulinaemic (0.4 mU/kg/min) euglycemic clamp and the methods employed included isotopical measurement of glucose turnover, indirect calorimetry, and the forearm technique. When compared to the control subjects the patients with acromegaly were preoperatively and in the basal state characterized by: 1) increased circulating concentrations of GH, insulin, and C-peptide (P less than 0.05); 2) increased plasma glucose (5.9 +/- 0.2 vs. 5.2 +/- 0.2 mmol/L), blood lactate (710 +/- 90 vs. 580 +/- 70 mumol/L), glucose turnover (2.34 +/- 0.12 vs. 1.93 +/- 0.12 mg/kg/min), and plasma lipid intermediates and a decreased forearm glucose uptake (0.06 +/- 0.02 vs. 0.19 +/- 0.04 mmol/L) (P less than 0.05); and 3) a 20% increase in energy expenditure, a 50% elevation of lipid oxidation rates, and a 130% elevation of nonoxidative glucose turnover (P less than 0.05). During the clamp the patients with active acromegaly were substantially resistant to the actions of insulin on both glucose and lipid metabolism. Following pituitary surgery all of these metabolic abnormalities were abolished. We conclude that active acromegaly is characterized by profound disturbances of not only glucose but also lipid metabolism, which in theory may precipitate the increased mortality in this disease. By showing that these abnormalities and the concomitant overall insulin resistance can be completely reversed our results may also have important implications for other insulin-resistant states and for the potential therapeutic use of GH.

Expression of GLUT1 and GLUT4 glucose transporters in skeletal muscle of humans with insulin-dependent diabetes mellitus: regulatory effects of metabolic factors.

Insulin-dependent diabetes mellitus (IDDM) is associated with insulin deficiency and insulin-resistant glucose uptake in skeletal muscle. To investigate the molecular mechanisms for this insulin resistance, we examined the expression of GLUT1 and GLUT4, glucose transporter genes in vastus lateralis muscle from 20 IDDM subjects and 10 nondiabetic controls. Both groups had a mean age of 34 yr and were nonobese. Fasting free plasma insulin levels were similar in control and IDDM subjects but hemoglobin A1c (HbA1c), fasting plasma glucose and free fatty acid levels were significantly higher in IDDM subjects. Euglycemic clamp studies over a range of insulin concentrations in these IDDM subjects previously showed both decreased insulin sensitivity and decreased maximally insulin stimulated glucose utilization. In this study, Northern blotting of muscle ribonucleic acid (RNA) revealed a single 3.0-3.5 kb transcript for both GLUT1 and GLUT4 with no change in messenger RNA (mRNA) size or abundance with IDDM. In IDDM subjects, GLUT1 mRNA levels correlated positively with HbA1c whereas GLUT4 mRNA levels correlated negatively with fasting plasma glucose but not with HbA1c. Neither mRNA correlated with fasting plasma insulin or free fatty acid levels or with daily insulin dose. Immunoblotting of total muscle membranes for GLUT4 showed a single band of mol mass of approximately 45 kilodaltons with no change in size or abundance with IDDM. There was no significant correlation between GLUT4 polypeptide levels and HbA1c, fasting plasma glucose, insulin, or free fatty acids, daily insulin dose, duration of diabetes, or subject age but in IDDM subjects GLUT4 protein levels correlated negatively with body mass index. Thus, impaired expression of glucose transporters in muscle is not essential for the pathogenesis of insulin-resistant glucose uptake in IDDM. No direct regulatory role of chronic glycemic control or plasma insulin levels on GLUT4 expression is evident. In contrast, recent ambient glucose levels may affect levels of GLUT4 mRNA but not GLUT4 protein, suggesting important posttranscriptional regulation of this protein. Since glucose transport has been shown to be rate limiting for glucose utilization in muscle in IDDM, these results suggest impaired translocation or activation of glucose transporters in IDDM.

Effects of perindopril on insulin sensitivity and plasma lipid profile in hypertensive non-insulin-dependent diabetic patients.

About 40% of patients with non-insulin-dependent diabetes (NIDDM) have hypertension, which in turn may contribute to their enhanced risk for cardiovascular diseases. However, a number of antihypertensive agents tend to cause a deterioration in the control of diabetes. The present study was designed to elucidate whether treatment with perindopril (a new angiotensin-converting enzyme [ACE] inhibitor) affects plasma lipid metabolism, glucose homeostasis, and insulin sensitivity. Ten patients with NIDDM and moderate hypertension were studied in a double-blind, placebo-controlled, crossover study encompassing 6 weeks of placebo treatment and 6 weeks of perindopril treatment given in random order. Mean systolic/diastolic blood pressure was 162/94 +/- 6/3 mm Hg during placebo treatment versus 157/91 +/- 5/2 mm Hg during perindopril therapy. Plasma levels of free fatty acids, triglycerides, high density lipoprotein (HDL) cholesterol, and total cholesterol were similar during placebo and perindopril treatment. Oral glucose tolerance tests showed similar responses of plasma glucose, serum insulin, and serum C peptide following placebo and perindopril treatment. Insulin sensitivity estimated with an intravenous insulin tolerance test (IVITT) was unchanged by perindopril therapy (KIVITT: 0.014 +/- 0.001 min-1 [placebo] versus 0.015 +/- 0.003 min-1 [perindopril], difference not significant. In conclusion, treatment with perindopril in NIDDM patients had no adverse effects on plasma lipids, glucose tolerance, or insulin sensitivity.

Effects of glucose and insulin on development of impaired insulin action in muscle.

Rat hindquarters were perfused for 2 h with either 0, 5, or 25 mM glucose in combination with either 0, 50, or 20,000 microU insulin/ml, whereupon responsiveness of glucose uptake to 20,000 microU insulin/ml and 25 mM glucose was measured. Perfusion with 25 mM glucose and 20,000 microU insulin/ml resulted in an initial glucose uptake of 43.6 +/- 3.9 mumol.g-1.h-1, which decreased to 18.7 +/- 1.6 mumol.g-1.h-1 after 2 h (P less than 0.001). Omission of glucose from the perfusate prevented the decrease in responsiveness, whereas 5 mM glucose caused a lesser decrease (to 28.3 +/- 2.2 mumol.g-1.h-1). At 0 and 50 microU insulin/ml the effects of glucose were present but were less pronounced. The decrease in insulin responsiveness of glucose uptake (55%) was accompanied by a lesser decrease (29%) in muscle glucose transport, whereas glucose transport in muscle membrane vesicles, muscle insulin binding, and insulin receptor tyrosine kinase activity were unchanged. Muscle glycogen synthase activity decreased (P less than 0.005) during perfusion with 25 mM glucose and 20,000 microU insulin/ml but did not decrease during perfusion with no glucose and 20,000 microU insulin/ml. It is concluded that insulin responsiveness of glucose uptake in muscle is decreased by exposure to glucose in a dose-dependent manner and the inhibitory effect of glucose is enhanced by simultaneous insulin exposure. The mechanism behind this insulin resistance could partly be explained by a decrease in muscle membrane glucose transport, possibly caused by changes in intracellular milieu.

Impaired expression of glycogen synthase mRNA in skeletal muscle of NIDDM patients.

Based on recent studies of the abnormal physiology and biochemistry of the glycogen synthesis in skeletal muscle of non-insulin-dependent diabetes mellitus (NIDDM) patients and their first-degree relatives, the key enzyme of this pathway, glycogen synthase (GS), is considered a candidate gene in the pathogenesis of insulin resistance. Comparing matched groups of 14 NIDDM patients with 14 control subjects, we found that impaired insulin-stimulated nonoxidative glucose metabolism of peripheral tissue (P less than 0.02) and reduced total GS activity (P less than 0.05) of vastus lateralis muscle from patients with NIDDM were accompanied by a 39% reduction (P less than 0.02) in the steady state level of GS mRNA per microgram DNA of muscle. In both diabetic and control subjects, the mRNA expression of GS was unaffected after euglycemic-hyperinsulinemic clamp for 4 h. With single-stranded conformation polymorphism analysis of the entire coding sequence of the GS gene, we were unable to detect any genetic variants in a subset of eight NIDDM patients. We conclude that abnormal pretranslational regulation of the GS gene may contribute to impaired glycogen synthesis of muscle in NIDDM. Our studies give no evidence for structural changes in the coding region of the GS gene, and it is unknown if the decreased mRNA expression is due to impaired transcription or accelerated degradation of the transcript.

Regional differences in triglyceride breakdown in human adipose tissue: effects of catecholamines, insulin, and prostaglandin E2.

Regional variation of adipose tissue triglyceride breakdown (lipolysis) has been suggested to play a role for the health consequences of some forms of obesity. Thus, in the present study we investigated the regulation of lipolysis in isolated adipocytes obtained from different fat depots in females. Intra-abdominal adipose tissue (omental) and subcutaneous abdominal adipose tissue were obtained from the same individuals undergoing abdominal surgery (n = 9); in addition, adipocytes from the subcutaneous gluteal region (n = 12) and from mammary adipose tissue (n = 5) were investigated. The lipolytic/antilipolytic properties of epinephrine (EPI), insulin, clonidine, and prostaglandin E2 (PGE2) were investigated. The most prominent observation was that EPI had none or only minor lipolytic effect in adipocytes from the subcutaneous regions, but significantly enhanced lipolysis by approximately 500% in omental adipocytes (P less than .001). In the presence of the alpha 2-adrenergic antagonist, yohimbine, EPI had similar stimulatory effects (fourfold to fivefold) in all fat depots. The antilipolytic compounds, insulin and clonidine, had greatly reduced antilipolytic properties in omental adipocytes as compared with subcutaneous adipocytes (P less than .01 and P less than .05, respectively). On the other hand, PGE2 had similar antilipolytic properties in adipocytes from the various depots. In conclusion, we found great regional variation in the regulation of lipolysis. Particularly, EPI was much more lipolytic in omental adipocytes than in subcutaneous adipocytes, mainly due to an enhanced functional alpha 2-receptor activity in subcutaneous adipocytes. These in vitro data suggest that free fatty acids (FFA) are more readily mobilized from omental adipose tissue than from subcutaneous adipose tissue.

Effects of hyperinsulinemia and hyperglycemia on insulin receptor function and glycogen synthase activation in skeletal muscle of normal man.

Insulin receptor function, glycogen synthase activity, and activation by phosphatases were studied in biopsies of human skeletal muscle under conditions of hyperglycemia and/or hyperinsulinemia for 150 minutes. Twenty-one healthy volunteers underwent either (A) a hyperinsulinemic, euglycemic clamp (serum insulin, 160.0 +/- 7.7 mU/L; plasma glucose, 4.9 +/- 0.1 mmol/L; n = 9), (B) a hyperglycemic clamp during normoinsulinemia (serum insulin, 18.1 +/- 3.3 mU/L; plasma glucose, 12.9 +/- 0.2 mmol/L; n = 6), or (C) a combined hyperinsulinemic, hyperglycemic clamp (serum insulin, 158.3 +/- 15.0 mU/L; plasma glucose, 11.4 +/- 0.8 mmol/L; n = 6). During all studies, the endogenous insulin secretion was inhibited with somatostatin. Insulin binding and kinase activity of insulin receptors solubilized from vastus lateralis muscle biopsies were unaffected by hyperglycemia and/or hyperinsulinemia. Hyperinsulinemia activated the muscle glycogen synthase with a decrease in the half-maximal activation constant (A0.5) for glucose-6-phosphate (G6P) from 0.53 +/- 0.04 to 0.21 +/- 0.02 mmol/L (study A, P less than .02) and from 0.53 +/- 0.06 to 0.19 +/- 0.05 mmol/L (study C, P less than .03). In addition, the rate of glycogen synthase activation by phosphatases increased from 0.078 +/- 0.017 to 0.134 +/- 0.029 U/min/mg protein (study A, P less than .03) and from 0.082 +/- 0.013 to 0.145 +/- 0.033 U/min/mg protein (study C, P = .05). Hyperglycemia during normoinsulinemia did not affect A0.5 or phosphatase activity. In conclusion, (1) hyperinsulinemia for 2 1/2 hours increases glycogen synthase activity and activation by phosphatases independently on the glycemia; and (2) insulin receptor binding and basal and insulin-stimulated receptor kinase activity are not modified during short-term hyperinsulinemia and/or hyperglycemia.

Effects of growth hormone on fuel utilization and muscle glycogen synthase activity in normal humans.

To examine the insulin antagonistic effects of growth hormone (GH), seven healthy subjects underwent, in random order, two 5-h euglycemic clamp studies with moderate hyperinsulinemia. A GH infusion (45 ng.kg-1.min-1) was given throughout one of the studies. GH inhibited the insulin-stimulated glucose disposal by 27% from 4.4 +/- 0.7 to 3.3 +/- 0.4 mg.kg-1.min-1 (P less than 0.02) and raised the nonprotein energy expenditures (NPEE) from 18.7 +/- 0.5 to 20.5 +/- 0.3 kcal.kg-1.24 h-1 (P less than 0.03). Lipid oxidation contributed 71.7 +/- 5.6% of NPEE during the GH infusion as compared with 48.7 +/- 5.2% during the control clamp (P less than 0.02). In skeletal muscle biopsies, insulin binding to wheat germ agglutinin-purified insulin receptors and insulin receptor kinase activity were unaffected by GH infusion. Glycogen synthase activation by insulin was inhibited by 41% during the GH clamp (fractional velocity 14.1 +/- 2.5 vs. 8.3 +/- 1.4%, P less than 0.03). In conclusion, GH 1) increases energy expenditures and inhibits glucose oxidation in favor of an increased lipid oxidation, and 2) inhibits insulin-mediated activation of the glycogen synthase in skeletal muscle biopsies by a mechanism distal to insulin receptor binding and kinase activity.