Insulin receptor autophosphorylation in cultured myoblasts correlates to glucose disposal in Pima Indians.
(9/1573)
In a previous study [Youngren, J. F., I. D. Goldfire, and R. E. Pratley. Am. J. Physiol. 273 (Endocrinol. Metab. 36): E276-E283, 1997] of skeletal muscle biopsies from insulin-resistant, nondiabetic Pima Indians, we demonstrated that diminished insulin receptor (IR) autophosphorylation correlated with in vivo insulin resistance. In the present study, to determine whether decreased IR function is a primary trait of muscle, and not secondary to an altered in vivo environment, we cultured myoblasts from 17 nondiabetic Pima Indians in whom insulin-stimulated glucose disposal (M) was measured during hyperinsulinemic-euglycemic glucose clamps. Myoblast IR autophosphorylation was determined by a highly sensitive ELISA. IR autophosphorylation directly correlated with M (r = 0.56, P = 0.02) and inversely correlated with the fasting plasma insulin (r = -0.58, P < 0.05). The relationship between M and IR autophosphorylation remained significant after M was adjusted for the effects of percent body fat (partial r = 0.53, P < 0.04). The relationship between insulin resistance and the capacity for myoblast IR autophosphorylation in nondiabetic Pima Indians suggests that variations in IR-signaling capacity may be intrinsic characteristics of muscle that contribute to the genetic component determining insulin action in this population. (+info)
Role of the human kidney in glucose counterregulation.
(10/1573)
Animal experiments indicate that the kidney may play an important role in glucose counterregulation. Because the human kidney normally takes up and releases glucose, and since patients with end-stage renal disease are prone to hypoglycemia, we examined whether the kidney is also involved in human glucose counterregulation. Accordingly, we compared renal glucose release (RGR) and uptake (RGU) during 4-h hyperinsulinemic-hypoglycemic (approximately 3.2 mmol/l, n = 9) and -euglycemic (approximately 5 mmol/l, n = 10) control clamp experiments in normal postabsorptive subjects. A combination of renal balance and isotopic ([3H]glucose, [14C]glutamine) techniques was used, which permitted hepatic glucose release (HGR) and glutamine gluconeogenesis to be calculated as the difference between systemic (overall) and renal values. In both experiments, infusion of insulin increased plasma insulin comparably (approximately 210 pmol/l). In euglycemic control experiments, RGR and HGR decreased more than 50% (both P<0.001) and RGU increased approximately 35% (P = 0.02). In hypoglycemic experiments, both HGR (P = 0.034) and RGR (P<0.001) increased to a comparable extent (1.69+/-0.47 and 1.67+/-0.15 pmol x kg-(-1) x min(-1), respectively, P = 0.96) above rates observed in control experiments; hepatic and renal glutamine gluconeogenesis increased by 0.19+/-0.06 (P<0.008) and 0.30+/-0.07 pmol x kg(-1) x min(-1) (P< 0.001), respectively. RGU decreased by 65% compared with control experiments (P<0.001), so that renal glucose balance changed from a net uptake of 80+/-19 micromol/min to a net release of 130+/-9 micromol/min, P< 0.001. These observations provide evidence that the kidney may play an important role in human glucose counterregulation. (+info)
Glucagon-like peptide 1 increases insulin sensitivity in depancreatized dogs.
(11/1573)
To determine whether glucagon-like peptide (GLP)-1 increases insulin sensitivity in addition to stimulating insulin secretion, we studied totally depancreatized dogs to eliminate GLP-1's incretin effect. Somatostatin was infused (0.8 microg x kg(-1) x min(-1)) to inhibit extrapancreatic glucagon in dogs, and basal glucagon was restored by intraportal infusion (0.65 ng x kg(-1) x min(-1)). To simulate the residual intraportal insulin secretion in type 2 diabetes, basal intraportal insulin infusion was given to obtain plasma glucose concentrations of approximately 10 mmol/l. Glucose was clamped at this level for the remainder of the experiment, which included peripheral insulin infusion (high dose, 5.4 pmol x kg(-1) x min(-1), or low dose, 0.75 pmol x kg(-1) x min(-1)) with or without GLP-1(7-36) amide (1.5 pmol x kg(-1) x min(-1)). Glucose production and utilization were measured with 3-[3H]glucose, using radiolabeled glucose infusates. In 12 paired experiments with six dogs at the high insulin dose, GLP-1 infusion resulted in higher glucose requirements than saline (60.9+/-11.0 vs. 43.6+/-8.3 micromol x kg(-1) x min(-1), P< 0.001), because of greater glucose utilization (72.6+/-11.0 vs. 56.8+/-9.7 micromol x kg(-1) x min(-1), P<0.001), whereas the suppression of glucose production was not affected by GLP-1. Free fatty acids (FFAs) were significantly lower with GLP-1 than saline (375.3+/-103.0 vs. 524.4+/-101.1 micromol/l, P<0.01), as was glycerol (77.9+/-17.5 vs. 125.6+/-51.8 micromol/l, P<0.05). GLP-1 receptor gene expression was found using reverse transcriptase-polymerase chain reaction of poly(A)-selected RNA in muscle and adipose tissue, but not in liver. Low levels of GLP-1 receptor gene expression were also found in adipose tissue using Northern blotting. In 10 paired experiments with five dogs at the low insulin dose, GLP-1 infusion did not affect glucose utilization or FFA and glycerol suppression when compared with saline, suggesting that GLP-1's effect on insulin action was dependent on the insulin dose. In conclusion, in depancreatized dogs, GLP-1 potentiates insulin-stimulated glucose utilization, an effect that might be contributed in part by GLP-1 potentiation of insulin's antilipolytic action. (+info)
Hepatic insulin resistance and defects in substrate utilization in cystic fibrosis.
(12/1573)
Patients with cystic fibrosis (CF)-related diabetes (CFRD) have clinical features of both type 1 and type 2 diabetes. Past studies have documented peripheral insulin resistance in CF, and some studies have noted high hepatic glucose production (HGP) in CF patients. We hypothesized that patients with CF, similar to patients with type 2 diabetes, have hepatic insulin resistance. Cystic fibrosis is a catabolic condition, yet the etiology of catabolism is poorly understood. De novo lipogenesis is energy wasteful and precludes ketogenesis. Patients with CFRD rarely develop ketogenesis, despite insulin deficiency. We speculated that CF patients have de novo lipogenesis, and therefore evaluated substrate utilization in CF. Using [6,6-2H2]glucose and a three-step hyperinsulinemic-euglycemic clamp, we measured HGP in 29 adult CF subjects and 18 control volunteers. Using indirect calorimetry, we measured lipid oxidation, oxidative glucose metabolism, and resting energy expenditure at baseline and at high levels of insulin. All subjects were characterized by oral glucose tolerance testing (OGTT) and National Diabetes Data Group criteria. The CF subjects had increased HGP when compared with control subjects (CF, 3.5+/-0.6; control, 2.5+/-0.5 mg x kg(-1) x h(-1); P = 0.002). Baseline HGP correlated with glucose levels obtained 2 h after a glucose load given for OGTT (r = 0.69, P = 0.001). Suppression of HGP by insulin was significantly less in all CF subgroups than in control subjects at peripheral insulin levels of 16 and 29 microU/ml. At peripheral insulin levels of 100 microU/ml and 198 microU/ml, there was no difference in insulin suppression of HGP between CF and control subjects. At baseline, there was no significant difference between control and CF subjects for glucose or lipid oxidation. During maximum insulin stimulation, there was a greater tendency for nonoxidative glucose metabolism in all CF subjects. The CF subjects with abnormal glucose tolerance also had de novo lipogenesis. Our results indicate that CF patients have several defects in substrate utilization, including de novo lipogenesis. Furthermore, these results suggest that high hepatic glucose production and hepatic insulin resistance contribute to the high incidence of abnormal glucose tolerance in CF. (+info)
Allosteric regulation of glycogen synthase and hexokinase by glucosamine-6-phosphate during glucosamine-induced insulin resistance in skeletal muscle and heart.
(13/1573)
Glucosamine infusion induces insulin resistance in vivo, but the effect of glucosamine on intracellular metabolites of the hexosamine pathway, especially glucosamine-6-phosphate (GlcN6P) is unknown. Because of the structural similarity of glucose-6-phosphate (G-6-P) and GlcN6P, we hypothesized that accumulation of this metabolite might alter the activities of enzymes such as glycogen synthase and hexokinase. We infused glucosamine (30 micromol x kg(-1) x min(-1)) to induce insulin resistance in rats during a euglycemic-hyperinsulinemic clamp. Glucosamine induced whole-body insulin resistance, which was apparent after 90 min and continued progressively for 360 min. Despite inducing severe whole-body insulin resistance and decrease in glycogen synthase fractional activity in rectus abdominis muscle (69+/-3 vs. 83+/-1%, P<0.01) and heart (7+/-1 vs. 32+/-4%, P<0.001), glucosamine did not change the glycogen content in rectus and even increased it in the heart (209+/-13 vs. 117+/-9 mmol/kg dry wt, P<0.001). Glucosamine increased tissue concentrations of UDP-GlcNAc 4.4- and 4.6-fold in rectus abdominis and heart, respectively. However, GlcN6P concentrations increased 500- and 700-fold in glucosamine-infused animals in rectus abdominis (590+/-80 vs. 1.2+/-0.1 micromol/kg wet wt, P<0.001) and heart (7,703+/-993 vs. 11.2+/-2.3 micromol/kg wet wt, P<0.001). To assess the possible significance of GlcN6P accumulation, we measured the effect of GlcN6P on glycogen synthase and hexokinase activity in vitro. At the GlcN6P concentrations measured in rectus abdominis and heart in vivo, glycogen synthase was activated by 21 and 542%, while similar concentrations inhibited hexokinase activity by 5 and 46%, respectively. This study demonstrates that infusion of glucosamine during a euglycemic-hyperinsulinemic clamp results in marked accumulation of intracellular GlcN6P. The GlcN6P concentrations in the heart and rectus abdominis muscle reach levels sufficient to cause allosteric activation of glycogen synthase and inhibition of hexokinase. (+info)
Association of increased intramyocellular lipid content with insulin resistance in lean nondiabetic offspring of type 2 diabetic subjects.
(14/1573)
Insulin resistance plays an important role in the pathogenesis of type 2 diabetes; however, the multiple mechanisms causing insulin resistance are not yet fully understood. The aim of this study was to explore the possible contribution of intramyocellular lipid content in the pathogenesis of skeletal muscle insulin resistance. We compared insulin-resistant and insulin-sensitive subjects. To meet stringent matching criteria for other known confounders of insulin resistance, these individuals were selected from an extensively metabolically characterized group of 280 first-degree relatives of type 2 diabetic subjects. Some 13 lean insulin-resistant and 13 lean insulin-sensitive subjects were matched for sex, age, BMI, percent body fat, physical fitness, and waist-to-hip ratio. Insulin sensitivity was determined by the hyperinsulinemic-euglycemic clamp method (for insulin-resistant subjects, glucose metabolic clearance rate [MCR] was 5.77+/-0.28 ml x kg(-1) x min(-1) [mean +/- SE]; for insulin-sensitive subjects, MCR was 10.15+/-0.7 ml x kg(-1) x min(-1); P<0.002). Proton magnetic resonance spectroscopy (MRS) was used to measure intramyocellular lipid content (IMCL) in both groups. MRS studies demonstrated that in soleus muscle, IMCL was increased by 84% (11.8+/-1.6 vs. 6.4+/-0.59 arbitrary units; P = 0.008 ), and in tibialis anterior muscle, IMCL was increased by 57% (3.26+/-0.36 vs. 2.08+/-0.3 arbitrary units; P = 0.017) in the insulin-resistant offspring, whereas the extramyocellular lipid content and total muscle lipid content were not statistically different between the two groups. These data demonstrate that in these well-matched groups of lean subjects, IMCL is increased in insulin-resistant offspring of type 2 diabetic subjects when compared with an insulin-sensitive group matched for age, BMI, body fat distribution, percent body fat, and degree of physical fitness. These results indicate that increased IMCL represents an early abnormality in the pathogenesis of insulin resistance and suggest that increased IMCL may contribute to the defective glucose uptake in skeletal muscle in insulin-resistant subjects. (+info)
Activation of the tissue factor pathway of blood coagulation during prolonged hyperglycemia in young healthy men.
(15/1573)
Patients with diabetes have an increased prevalence of premature atherosclerotic vascular disease, and alterations in plasma coagulation proteins have been incriminated as a possible cause. The roles of hyperglycemia and hyperinsulinemia in the pathogenesis of these changes are unknown. To examine the effects of prolonged hyperglycemia and of selective hyperinsulinemia on the tissue factor pathway of blood coagulation, nine healthy young men were infused with glucose to maintain levels at 11.1 mmol/l (approximately 200 mg/dl) for 18-72 h (hyperglycemia-hyperinsulinemia group). Five normal men were infused with regular insulin to maintain levels comparable to that in the previous group (900 pmol/l, approximately 150 microU/ml) and with glucose to maintain levels at 5.6 mmol/l (approximately 100 mg/dl) (euglycemia-hyperinsulinemia group). Measured were plasma activated factor VII activity (FVIIa), FVII coagulant (FVIIC) activity, FVIII coagulant (FVIIIC) activity, tissue factor pathway inhibitor (TFPI) antigen, and thrombin markers; and serum glucose, insulin, and electrolytes. Plasma FVIIa, FVIIC, FVIIIC, and TFPI rose during hyperglycemic-hyperinsulinemia but not during euglycemic-hyperinsulinemia. Markers of thrombin generation rose transiently and inconsistently during hyperglycemia-hyperinsulinemia. We concluded that in normal subjects, hyperglycemia-hyperinsulinemia induced activation of the tissue factor pathway, reflected by increases in plasma FVIIa, FVIIC, and TFPI. This activation was independent of hyperinsulinemia, hypertriglyceridemia, and hyperosmolality. The elevations in plasma coagulation factors during hyperglycemia-hyperinsulinemia, characteristic of type 2 diabetes, may constitute a potential for enhanced thrombin generation and thrombosis when triggered by exposure of tissue factor, such as during arterial plaque rupture. (+info)
Homeostasis model assessment as a clinical index of insulin resistance in type 2 diabetic patients treated with sulfonylureas.
(16/1573)
OBJECTIVE: To investigate whether the insulin resistance index (IR) assessed by homeostasis model assessment (HOMA) is associated with the insulin resistance index assessed by euglycemic-hyperinsulinemic clamp (clamp IR) in type 2 diabetic patients who received sulfonylureas (SUs), as well as in those treated by diet alone. RESEARCH DESIGN AND METHODS: Retrospectively, the association between HOMA IR and clamp IR was analyzed in 80 type 2 diabetic subjects (53 subjects treated with SUs and 27 subjects treated with diet alone). The 80 subjects, selected because they had not received insulin therapy, were among 111 diabetic participants in a clamp study for evaluation of insulin resistance from May 1993 to December 1997 in Osaka City University Hospital. RESULTS: The HOMA IR showed a hyperbolic relationship with clamp IR. The log-transformed HOMA IR (all subjects, r = -0.725, P < 0.0001; SU group, r = -0.727, P < 0.0001; diet group, r = -0.747, P < 0.0001) correlated more strongly with clamp IR than did HOMA IR per se (all subjects, r = -0.594, P < 0.0001; SU group, r = -0.640, P < 0.0001; diet group, r = -0.632, P = 0.0004). The univariate regression line between log-transformed HOMA IR and clamp IR in the SU group did not differ from that in the diet group (slope, -6.866 vs. -5.120, P > 0.05; intercept, 6.566 vs. 5.478, P > 0.05). Stepwise multiple regression analyses demonstrated that the log-transformed HOMA IR was the strongest independent contributor to clamp IR (R2 = 0.640, P < 0.0001). CONCLUSIONS: The HOMA IR strongly correlated with the clamp IR in type 2 diabetic patients treated with SUs as well as in those treated with diet alone. (+info)