Important role of the hepatic vagus nerve in glucose uptake and production by the liver

We examined the role of the hepatic vagus nerve in hepatic and peripheral glucose metabolism. To assess endogenous glucose production (EGP), hepatic uptake of first-pass glucose infused intraportally (HGU), and the metabolic clearance rate of glucose (MCR), rats were subjected to hepatic vagotomy (HV, n = 7) or sham operation (SH, n = 8), after 10 days, they were then subjected to a euglycemic-hyperinsulinemic clamp together with a portal glucose load in the 24-hour fasting state. Metabolic parameters were determined by the dual-tracer method using stable isotopes. During the experiment, [6,6-2H2]glucose was continuously infused into the peripheral vein. To maintain euglycemia (4.5 mmol/L), insulin (54 pmol x kg(-1) x min(-1)) and glucose were infused peripherally after the 90-minute tracer equilibration and 30-minute basal periods, and glucose containing 5% enriched [U-13C]glucose was infused intraportally (50 micromol x kg(-1) x min(-1)) for 120 minutes (clamp period). EGP was significantly higher in HV rats versus SH rats during the basal period (64.3 +/- 7.6 v 43.6 +/- 5.3 micromol x kg(-1) x min(-1), P < .005)) and was comparable to EGP in SH rats during the clamp period (9.3 +/- 21.5 v 1.1 +/- 11.7 micromol x kg(-1) x min(-1)). HGU was reduced in HV rats compared with SH rats during portal glucose infusion (5.9 +/- 2.4 v 10.1 +/- 3.2 micromol x kg(-1) x min(-1)). The MCR in HV rats was significantly higher than in SH rats in the basal period (11.0 +/- 2.0 v 7.9 +/- 0.8 mL x kg(-1) x min(-1), P < .01)) and was comparable to the MCR in SH rats during the clamp period (41.9 +/- 10.0 and 36.6 +/- 5.7 mL x kg(-1) x min(-1)). We conclude that innervation of the hepatic vagus nerve is important for the regulation of hepatic glucose production in the postabsorptive state and HGU in the postprandial state.     

Plasma adiponectin level is associated with insulin-stimulated nonoxidative glucose disposal

CONTEXT: Impaired nonoxidative glucose disposal and decrease in mitochondrial glucose oxidation both contribute to insulin resistance in diabetic subjects. OBJECTIVE: In the present study, we investigated whether plasma adiponectin is associated with glucose oxidation and nonoxidative glucose disposal in subjects with and without type 2 diabetes. DESIGN: Euglycemic-hyperinsulinemic clamp was performed in 42 type 2 diabetic (T2DM) and 13 nondiabetic (non-DM) subjects. The whole-body glucose disposal rate (GDR) was evaluated as the mean of the glucose infusion rate during steady state of the clamp. Glucose and fat oxidation rates were assessed by indirect calorimetry, and nonoxidative glucose disposal rate was calculated by subtracting glucose oxidation rate from GDR. RESULTS: Plasma adiponectin level was significantly lower in T2DM than non-DM (2.87 +/- 1.40 vs. 3.96 +/- 2.39 microg/ml, P = 0.045). GDR (3.39 +/- 1.53 vs. 4.83 +/- 1.70 mg/kg x min, P = 0.006) and nonoxidative glucose disposal rate (1.89 +/- 1.39 vs. 3.11 +/- 1.76 mg/kg x min, P = 0.012) were significantly lower in T2DM, compared with non-DM, although no difference was found in glucose oxidation rate between the two groups. In all subjects, plasma adiponectin level was positively correlated with GDR (r = 0.351, P = 0.009) and nonoxidative glucose disposal rate (r = 0.324, P = 0.016) but not glucose oxidation rate. There was no significant correlation between plasma adiponectin level and fat oxidation, either before or during the clamp. CONCLUSIONS: In conclusion, plasma adiponectin level is associated with nonoxidative glucose disposal, which is reduced in type 2 diabetic subjects. Our results suggest that adiponectin controls insulin sensitivity by modulating the glycogen synthetic process in human skeletal muscle.     

Insulin action and skeletal muscle blood flow in patients with Type 1 diabetes and microalbuminuria

Our objective was to determine whether Type 1 diabetic patients with microalbuminuria are less sensitive to the effects of insulin on glucose metabolism and skeletal muscle blood flow, compared to those with normal albumin excretion, after careful matching for confounding variables. We recruited 10 normotensive Type 1 diabetic patients with microalbuminuria and 11 with normoalbuminuria matched for age, sex, body mass index, duration of diabetes and HbA(1c). Peripheral and hepatic insulin action was assessed using a two-step euglycaemic hyperinsulinaemic clamp (2 h at 0.4 mU x kg(-1) x min(-1), 2 h at 2.0 mU x kg(-1) x min(-1)) combined with isotope dilution methodology. Skeletal muscle blood flow was determined by venous occlusion plethysmography. During the clamps, glucose infusion rates required to maintain euglycaemia were similar in the microalbuminuric subjects and controls (step 1, 8.2+/-1.4 (SE) vs 9.2+/-1.3 micromol x kg(-1) x min(-1): step 2, 30.9+/-2.7 vs 32.0+/-3.8 micromol x kg(-1) x min(-1)), as was hepatic glucose production basally and at steady state in step 1. In step 2, hepatic glucose production was lower in the microalbuminuric group (2.9+/-0.9 vs 6.4+/-0.7 micromol x kg(-1) x min(-1), P=0.005). During step 2, skeletal muscle blood flow increased significantly above baseline in the normoalbuminuric group (4.1+/-0.5 vs 3.2+/-0.4 ml x 100-ml(-1) x min(-1), P=0.01) but not in the microalbuminuric group (2.4+/-0.3 vs 2.3+/-0.4 ml x 100-ml(-1) x min(-1)). In conclusion, microalbuminuria in Type 1 diabetes was found to be associated with impairment of insulin-mediated skeletal muscle blood flow, but not with insulin resistance.     

Acute elevation of free fatty acids impairs hepatic glucose uptake in conscious rats

To investigate the dose-dependent effect of free fatty acid (FFA) on the hepatic glucose uptake (HGU), we determined hepatic glucose fluxes by a dual tracer technique during the basal state and euglycemic hyperinsulinemic clamp combined with a portal glucose load in three groups of rats given saline (saline), low-dose lipid (lipid-L), or high-dose lipid infusion (lipid-H). In the basal state, lipid infusion dose-dependently increased plasma FFA (saline, 400 +/- 50; lipid-L, 550 +/- 30; lipid-H, 1700 +/- 270 micromol l(-1); mean +/- S.E). Endogenous glucose production (EGP) in lipid-H was 63.5 +/- 5.5 micromol kg(-1) min(-1) and significantly higher than in the saline and lipid-L (40.2 +/- 2.9, 47.6 +/- 3.1 micromol kg(-1) min(-1), respectively). During euglycemic hyperinsulinemic clamp, plasma FFA decreased to 130 +/- 30 micromol l(-1) in saline, but remained at basal levels in lipid-L and lipid-H (470 +/- 30 and 1110 +/- 180 micromol l(-1), respectively). Insulin-suppressed EGP was complete in saline and lipid-L, but impaired in lipid-H (38.0 +/- 6.4 micromol kg(-1) min(-1)). Elevated FFA dose-dependently reduced HGU (saline, 12.2 +/- 0.9; lipid-L, 8.6 +/- 0.6; lipid-H, 4.7 +/- 1.4 micromol kg(-1) min(-1)). In conclusion, acutely elevated FFA impairs HGU as well as insulin-mediated suppression of EGP during hyperinsulinemic clamp with portal glucose loading. Impaired hepatic glucose uptake associated with elevated FFA may contribute to the development of insulin resistance in obesity and type 2 diabetes.     

The role of plasma fatty acid composition in endogenous glucose production in patients with type 2 diabetes mellitus

Hepatic insulin resistance and increased endogenous glucose production (EGP) are associated with increased plasma free fatty acids (FFA). However, the contribution of FFA composition to the regulation of EGP is not known. Six obese nondiabetic subjects and 6 patients with type 2 diabetes mellitus (DM2) were studied after an overnight and a 3-day fast. Plasma insulin concentrations after an overnight fast were similar in the DM2 and nondiabetic patients (88.8 +/- 26.4 v 57.6 +/- 12.6 pmol/L, not significant [NS]) despite increased plasma glucose (9.9 +/- 1.8 v 5.1 +/- 0.1 mmol/L, P <.01) and EGP (510.3 +/- 77.7 v 298.3 +/- 18.3 micromol x m(-2) x min(-1), P <.05) in the patients with DM2. Absolute rates of gluconeogenesis using the heavy water method were also increased in the patients with DM2 (346.8 +/- 74.9 v 198.8 +/- 16.4 micromol x m(-2). min(-1), P <.05). No differences were observed in plasma polyunsaturated fatty acids (PUFA) between the diabetic and nondiabetic subjects. However, total saturated fatty acid (SFA) concentrations (350 +/- 37.4 v 230.9 +/- 33.3 micromol/L, P <.02) were significantly increased in the diabetic subjects. Rates of EGP were correlated with total plasma FFA concentration (r =.71, P <.01) and the concentration of SFA (r =.71, P <.01), but not monounsaturated fatty acids or PUFA. Rates of gluconeogenesis were also correlated with plasma FFA (r =.64, P <.05) and SFA (r =.67, P <.05). We observed no relationship between EGP and either total FFA or fatty acid composition after a 3-day fast. We conclude that increases in EGP are associated with concentrations of plasma SFA after an overnight fast.     

Increased renal glucose metabolism in Type 1 diabetes mellitus.

AIMS: In poorly controlled diabetes, increased renal glucose uptake has been implicated in the pathogenesis of diabetic nephropathy by promoting nonenzymatic glycosylation of proteins, activation of protein kinase C, and increased polyol pathway flux. However, whether glucose uptake by the diabetic kidney is actually increased, especially in patients with Type 1 diabetes, is unclear. METHODS: To examine this question, we used a combination of net balance and isotopic techniques to compare renal glucose uptake in 12 subjects with Type 1 diabetes before and after restoration of near normoglycaemia by infusion of insulin with that in 15 postabsorptive nondiabetic volunteers. RESULTS: Prior to insulin infusion, the diabetic subjects were markedly hyperglycaemic (arterial glucose 15.8 +/- 0.9 vs. 4.4 +/- 0.1 mm) and their renal tissue glucose uptake (i.e. total glucose disappearance across the kidney minus glycosuria) was increased more than 2 1/2-fold (388 +/- 43 vs. 148 +/- 12 micromol/min, P < 0.001). This was wholly explained by the mass action effects of hyperglycaemia since the diabetic subjects had normal renal blood flow (1575 +/- 82 vs. 1492 +/- 68 mL/min, P = 0.46) and reduced renal tissue glucose fractional extraction (1.7 +/- 0.2 vs. 2.3 +/- 0.1%, P = 0.027). Insulin infusion for three hours, which restored near normoglycaemia (arterial glucose 7.6 +/- 0.7 mm), reduced renal tissue glucose uptake toward normal (258 +/- 41 micromol/min, P = 0.006) without altering renal blood flow (1557 +/- 110, P = 0.63) or renal tissue glucose fractional extraction (2.1 +/- 0.3%, P = 0.35). Renal and hepatic glucose release, which had been increased (419 +/- 49 and 960 +/- 54 vs. 204 +/- 9 and 734 +/- 32 micromol/min, both P < 0.001), were suppressed by insulin to 138 +/- 22 and 520 +/- 53 micromol/min, respectively (both P < 0.001). CONCLUSIONS: In poorly controlled Type 1 diabetes, renal glucose uptake is markedly increased, which provides a link between hyperglycaemia and biochemical processes implicated in the pathogenesis of diabetic nephropathy. Its reversal by restoration of near normoglycaemia with insulin may explain the benefit of intensive insulin therapy in preventing diabetic nephropathy.     

Down-regulation of insulin receptor substrates (IRS)-1 and IRS-2 and Src homologous and collagen-like protein Shc gene expression by insulin in skeletal muscle is not associated with insulin resistance or type 2 diabetes.

To examine whether altered gene expression of insulin receptor substrates (IRS)-1 and IRS-2 and Src homologous and collagen-like protein Shc is an inherited trait and is associated with muscle insulin resistance or type 2 diabetes, we measured mRNA levels of these genes by a relative quantitative RT-PCR method in muscle biopsies taken before and after an insulin clamp from 12 monozygotic twin pairs discordant for type 2 diabetes and 12 control subjects. Insulin-stimulated glucose uptake was decreased both in the diabetic and nondiabetic twin, compared with healthy control subjects (5.2 +/- 0.7 and 8.5 +/- 0.8 vs. 11.4 +/- 0.9 mg/kg x min(-1); P < 0.01 and P < 0.02, respectively). Basal mRNA levels of IRS-1, IRS-2, and Shc were similar in the diabetic and nondiabetic twins as well as in the control subjects. Insulin decreased mRNA expression of IRS-1 by 72% (from 0.75 +/- 0.06 to 0.21 +/- 0.04 relative units; P < 0.001), IRS-2 by 71% (from 0.55 +/- 0.10 to 0.16 +/- 0.08 relative units; P < 0.03), and Shc by 25% (from 0.95 +/- 0.04 to 0.71 +/- 0.04 relative units; P < 0.01) vs. baseline as demonstrated in the control subjects. The postclamp Shc mRNA level was slightly higher in the diabetic twins (P = 0.05) but similar in the nondiabetic twins, as compared with the control subjects, whereas postclamp IRS-1 and IRS-2 mRNA levels were similar between the study groups. There was an inverse correlation between postclamp Shc mRNA concentration and glucose uptake (r = -0.53, P = 0.01; n = 22) in the controls and nondiabetic twins. However, the decrease in Shc gene expression by insulin was not significantly different between the study groups. In conclusion, because insulin down-regulates IRS-1, IRS-2, and Shc gene expression in skeletal muscle in diabetic and nondiabetic monozygotic twins and control subjects to the same extent, it is unlikely that expression of these genes is an inherited trait or contributes to skeletal muscle insulin resistance.     

Intracellular partition of plasma glucose disposal in hypertensive and normotensive subjects with type 2 diabetes mellitus

The aim of this study was to ascertain whether the presence of hypertension conveys a more severe degree of insulin resistance in type 2 diabetes mellitus and, if so, which biochemical pathways are involved. We quantitated the rates of total glucose disposal, glycogen synthesis (GS), glycolysis, glucose oxidation, endogenous glucose production, and LOX in the basal state and during a 4-h euglycemic ( approximately 5 mM) hyperinsulinemic ( approximately 300 pM) clamp carried out in combination with a dual-tracer infusion ([(3)H]-3- and [(14)C]-U-D-glucose) and indirect calorimetry in 42 nonobese noninsulin-treated type 2 diabetic subjects (22 hypertensive and 20 normotensive) and 23 nonobese nondiabetic subjects (9 without and 14 with essential hypertension). Compared with normotensive controls, both groups of diabetic subjects were markedly insulin resistant. In the basal state, all glucose fluxes were similar in diabetic subjects with or without hypertension. During insulin infusion, total glucose disposal was significantly reduced in hypertensive diabetic subjects, compared with their normotensive counterparts (18.7 +/- 1.0 vs. 28.6 +/- 3.0 micromol/min.kg lean body mass; P < 0.01). This difference was almost entirely explained by a marked reduction in GS (4.5 +/- 2.0 vs. 12.5 +/- 3.3 micromol/min.kg lean body mass; P < 0.01). Endogenous glucose production was not different in the two diabetic groups during insulin infusion and was significantly higher than in normotensive controls. Lipid oxidation was less suppressed by hyperinsulinemia in hypertensive than in normotensive diabetic subjects (1.46 +/- 0.1 vs. 0.91 +/- 0.1 micromol/min.kg lean body mass; P < 0.01). Glucose fluxes were not significantly different in nondiabetic subjects with essential hypertension and in normotensive diabetic individuals. These results indicate that hypertension markedly aggravates insulin resistance featuring type 2 diabetes mellitus. The molecular defects underlying this phenomenon involve primarily GS.     

Insulin resistance in type 2 diabetes: association with truncal obesity,impaired fitness,and atypical malonyl coenzyme A regulation

Abdominal obesity and physical inactivity are associated with insulin resistance in humans and contribute to the development of type 2 diabetes. Likewise, sustained increases in the concentration of malonyl coenzyme A (CoA), an inhibitor of fatty-acid oxidation, have been observed in muscle in association with insulin resistance and type 2 diabetes in various rodents. In the present study, we assessed whether these factors are present in a defined population of slightly overweight (body mass index, 26.2 kg/m2), insulin-resistant patients with type 2 diabetes. Thirteen type 2 diabetic men and 17 sex-, age-, and body mass index-matched control subjects were evaluated. Insulin sensitivity was assessed during a two-step euglycemic insulin clamp (infusion of 0.25 and 1.0 mU/kg x min). The rates of glucose administered during the low-dose insulin clamp were 2.0 +/- 0.2 vs. 0.7 +/- 0.2 mg/kg body weight x min (P < 0.001) in the control and diabetic subjects, respectively; rates during the high-dose insulin clamp were 8.3 +/- 0.7 vs. 4.6 +/- 0.4 mg/kg body weight x min (P < 0.001) for controls and diabetic subjects. The diabetic patients had a significantly lower maximal oxygen uptake than control subjects (29.4 +/- 1.0 vs. 33.4 +/- 1.4 ml/kg x min; P = 0.03) and a greater total body fat mass (3.7 kg), mainly due to an increase in truncal fat (16.5 +/- 0.9 vs. 13.1 +/- 0.9 kg; P = 0.02). The plasma concentration of free fatty acid and the rate of fatty acid oxidation during the clamps were both higher in the diabetic subjects than the control subjects (P = 0.002-0.007). In addition, during the high-dose insulin clamp, the increase in cytosolic citrate and malate in muscle, which parallels and regulates malonyl CoA levels, was significantly less in the diabetic patients (P < 0.05 vs. P < 0.001). Despite this, a similar increase in the concentration of malonyl CoA was observed in the two groups, suggesting an abnormality in malonyl CoA regulation in the diabetic subjects. In conclusion, the results confirm that insulin sensitivity is decreased in slightly overweight men with mild type 2 diabetes and that this correlates closely with an increase in truncal fat mass and a decrease in physical fitness. Whether the unexpectedly high levels of malonyl CoA in muscle, together with the diminished suppression of plasma free fatty acid, explains the insulin resistance of the diabetic patients during the clamp remains to be determined.     

Exogenous insulin replacement in type 2 diabetes reverses excessive hepatic glucose release,but not excessive renal glucose release and impaired free fatty acid clearance

In type 2 diabetes renal and hepatic glucose release are increased and free fatty acids (FFA) clearance is reduced. Restoration of normoglycemia by exogenous insulin replacement normalizes overall glucose release and plasma FFA concentrations. However, it is unclear to what extent normalization of overall glucose release is due to suppression of hepatic (HGR) and renal glucose release (RGR) and whether the abnormal FFA clearance is improved. We therefore determined overall, renal, and hepatic glucose release, as well as systemic FFA release and clearance by tracer techniques in type 2 diabetic subjects with (DM(+)) and without (DM(-)) physiologic overnight insulin infusion and in nondiabetic volunteers (NV). Insulin infusion normalized plasma glucose (5.3 +/- 0.1 v 5.2 +/- 0.1 mmol/L in NV) and overall glucose release (10.1 +/- 0.7 v 10.6 +/- 0.4 micromol x kg(-1) x min(-1) in NV), (both P >.9). Values in DM(-) were 9.1 +/- 0.6 mmol/L and 14.6 +/- 0.8 micromol x kg(-1) x min(-1), respectively (both P <.001 v DM(+) and NV). The correction of overall glucose release in DM(+) was due to suppression of HGR to rates below normal (6.11 +/- 0.53 v 8.67 +/- 0.44 micromol x kg(-1) x min(-1) in NV, P <.03). RGR remained increased (3.91 +/- 0.38 v 1.90 +/- 0.28 micromol x kg(-1) x min(-1) in NV, P <.002) and was similar to DM(-) (3.97 +/- 0.33 micromol x kg(-1) x min(-1), P >.9). Insulin infusion also normalized plasma FFA levels (450 +/- 45 v 476 +/- 42 in NV, P >.9 and v613 +/- 33 micromol/L in DM(-), P <.04). This was due to suppression of FFA release to below normal (4.04 +/- 0.45 v 5.25 +/- 0.25 micromol x kg(-1) x min(-1) in NV, P <.04). Plasma FFA clearance remained reduced (7.2 +/- 1.0 v 11.4 +/- 1.2 mL x kg(-1) x min(-1) in NV, P <.04) and was similar to DM(-) (7.3 +/- 0.5 mL x kg(-1) x min(-1), P >.9). We conclude that in contrast to the excessive HGR, excessive RGR and impaired FFA clearance are not corrected by acute exogenous insulin replacement.     

Adipose tissue, hepatic, and skeletal muscle insulin sensitivity in extremely obese subjects with acanthosis nigricans

We evaluated insulin action in skeletal muscle (glucose disposal), liver (glucose production), and adipose tissue (lipolysis) in 5 extremely obese women with acanthosis nigricans (AN), who had normal oral glucose tolerance, and 5 healthy lean subjects, by using a 5-stage pancreatic clamp and stable isotopically labeled tracer infusion. Basal plasma insulin concentration was much greater in obese subjects with AN than lean subjects (54.8 +/- 4.5 vs 8.0 +/- 1.3 microU/mL, P < .001), but basal glucose and free fatty acid concentrations were similar in both groups. During stage 1 of the clamp, glucose rate of appearance (R(a)) (2.6 +/- 0.3 vs 3.7 +/- 0.3 micromol x kg FFM(-1) x min(-1), P = .02) and palmitate R(a) (2.4 +/- 0.6 vs 7.0 +/- 1.5 micromol x kg FFM(-1) x min(-1), P < .05) were greater in obese subjects with AN than lean subjects despite slightly greater plasma insulin concentration in subjects with AN (3.0 +/- 0.7 vs 1.1 +/- 0.4 microU/mL, P < .05). The area under the curve for palmitate R(a) (1867 +/- 501 vs 663 +/- 75 micromol x kg FFM(-1) x 600 min(-1), P = .03) and glucose R(a) (1920 +/- 374 vs 1032 +/- 88 micromol x kg FFM(-1) x 600 min(-1), P = .02) during the entire clamp procedure was greater in subjects with AN than lean subjects. During intermediate insulin conditions (plasma insulin, approximately 35 microU/mL), palmitate R(a) was 5-fold greater in subjects with AN than in lean subjects (2.6 +/- 1.1 vs 0.5 +/- 0.2 micromol x kg FFM(-1) x min(-1), P = .05). Maximal glucose disposal was markedly lower in obese subjects with AN than in lean subjects (13.0 +/- 0.8 vs 23.4 +/- 1.8 mg x kg FFM(-1) x min(-1), P = .01) despite greater peak plasma insulin concentration (1842 +/- 254 vs 598 +/- 38 microU/mL, P < .05). These data demonstrate obese young adults with AN have marked insulin resistance in multiple tissues. However, marked insulin hypersecretion can compensate for impaired insulin action, resulting in normal glucose and fatty acid metabolism during basal conditions.     

Hepatic insulin resistance in antipsychotic naive schizophrenic patients: stable isotope studies of glucose metabolism

OBJECTIVE: Our objective was to measure insulin sensitivity and body composition in antipsychotic-naive patients with DSM IV schizophrenia and/or schizoaffective disorder compared with matched controls. DESIGN: Seven antipsychotic medication-naive patients fulfilling the DSM IV A criteria for schizophrenia/schizoaffective disorder were matched for body mass index, age, and sex with seven control subjects. We measured endogenous glucose production and peripheral glucose disposal using a hyperinsulinemic euglycemic clamp (plasma insulin concentration approximately 200 pmol/liter) in combination with stable isotopes. Fat content and fat distribution were determined with a standardized single-slice computed tomography scan and whole body dual-energy x-ray absorptiometry. RESULTS: Endogenous glucose production during the clamp was 6.7 micromol/kg x min (sd 2.7) in patients vs. 4.1 micromol/kg x min (sd 1.6) in controls (P = 0.02) (95% confidence interval -5.2 to 0.006). Insulin-mediated peripheral glucose uptake was not different between patients and controls. The amount of sc abdominal fat in patients was 104.6 +/- 28.6 cm(3) and 63.7 +/- 28.0 cm(3) in controls (P = 0.04) (95% confidence interval 4.4-77.2). Intraabdominal fat and total fat mass were not significantly different. CONCLUSIONS: Antipsychotic medication-naive patients with schizophrenia or schizoaffective disorder display hepatic insulin resistance compared with matched controls. This finding cannot be attributed to differences in intraabdominal fat mass or other known factors associated with hepatic insulin resistance and suggests a direct link between schizophrenia and hepatic insulin resistance.     

Continuous subcutaneous insulin infusion therapy decreases insulin resistance in type 1 diabetes

The influence of continuous sc insulin infusion therapy for 6 weeks on sensitivity to insulin (euglycemic clamp technique) and hepatic glucose production (3-[3H]glucose technique) was measured in 10 type 1 diabetic patients whose mean duration of diabetes was 8 yr. Mean diurnal blood glucose fell from 8.5 +/- 0.8 (SEM) mmol/liter to 6.0 +/- 0.6 mmol/liter (P less than 0.05) and glycosylated hemoglobin from 10.5 +/- 0.4% to 8.7 +/- 0.3%. Insulin requirements declined by 23% from 47 +/- 4 U/day prepump to 36 +/- 2 U/day after 6 weeks of pump therapy (P less than 0.01). During the insulin clamp, plasma insulin was maintained at approximately 90 mU/liter and plasma glucose at approximately 5.0 mmol/liter in all studies. The rate of glucose metabolism in diabetic patients during conventional therapy (4.65 +/- 0.41 mg/kg X min) was 35% lower than in normal subjects (7.20 +/- 0.42 mg/kg X min, n = 14, P less than 0.001). After 6 weeks of pump therapy, total glucose uptake increased by 27% to 5.90 +/- 0.60 mg/kg X min, P less than 0.05 vs. prepump). This was still 18% lower than in the normal subjects (P less than 0.05). Basal hepatic glucose production in the diabetic patients during conventional therapy (3.07 +/- 0.14 mg/kg X min) was 70% higher than in the normal subjects (1.79 +/- 0.07 mg/kg X min, n = 7, P less than 0.001). After 6 weeks of pump therapy, hepatic glucose production fell to 2.48 +/- 0.19 mg/kg X min (P less than 0.05), which was still 40% higher than in the normal subjects (P less than 0.01). Basal hepatic glucose production was directly related to the fasting plasma glucose level (r = 0.67, P less than 0.001) and inversely proportional to fasting insulin concentration (r = -0.48, P less than 0.05) in the diabetic patients. Specific tracer insulin binding to erythrocytes in the diabetic patients (19.4 +/- 1.5%) was comparable to that in the normal subjects (19.6 +/- 1.2%) and remained unchanged during pump therapy. Thus the improved metabolic control resulting from pump therapy is associated with enhancement in sensitivity to insulin, and reduction in basal hepatic glucose production.     

Direct measurements of the permeability surface area for insulin and glucose in human skeletal muscle

To elucidate mechanisms regulating capillary transport of insulin and glucose, we directly calculated the permeability surface (PS) area product for glucose and insulin in muscle. Intramuscular microdialysis in combination with the forearm model and blood flow measurements was performed in healthy males, studied during an oral glucose tolerance test or during a one-step or two-step euglycemic hyperinsulinemic clamp. PS for glucose increased significantly from 0.29 +/- 0.1 to 0.64 +/- 0.2 ml/min.100 g after oral glucose tolerance test, and glucose uptake increased from 1.2 +/- 0.4 to 2.6 +/- 0.6 micro mol/min.100 g (P < 0.05). During one-step hyperinsulinemic clamp (plasma insulin, 1.962 pmol/liter), PS for glucose increased from 0.2 +/- 0.1 to 2.3 +/- 0.9 ml/min.100 g (P < 0.05), and glucose uptake increased from 0.6 +/- 0.2 to 5.0 +/- 1.4 micro mol/min.100 g (P < 0.05). During the two-step clamp (plasma insulin, 1380 +/- 408 and 3846 +/- 348 pmol/liter), the arterial-interstitial difference and PS for insulin were constant. The PS for glucose tended to increase (P = not significant), whereas skeletal muscle blood flow increased from 4.4 +/- 0.7 to 6.2 +/- 0.8 ml/min.100 ml (P < 0.05). The present data show that PS for glucose is markedly increased by oral glucose, whereas a further vasodilation exerted by high insulin concentrations may not be physiologically relevant for capillary delivery of either glucose or insulin in resting muscle.     

Oral contraception and insulin sensitivity: in vivo assessment in normal women and women with previous gestational diabetes

The sensitivity to insulin (euglycemic clamp technique) was assessed in previous gestational diabetic women (n = 6) and nondiabetic women (n = 6) before and twice during low-dose triphasic oral contraceptive administration (ethinyl estradiol and levonorgestrel) for 6 months. Both groups had normal plasma glucose and insulin levels during oral glucose tolerance tests before and during treatment. In vivo peripheral insulin action was measured during insulin infusion of 40 mU/m2 X min with plasma glucose clamped at fasting levels. Before treatment glucose infusion rates were identical in both groups [1.56 +/- 0.12 (SEM) mmol/m2 X min and 1.51 +/- 0.09 mmol/m2 X min, respectively]. After hormonal treatment for 6 months the amount of glucose infused decreased significantly in the previously gestational diabetic women (1.10 +/- 0.12 mmol/m2 X min, P = 0.01), whereas the decrease was less pronounced in the nondiabetic women (1.30 +/- 0.22 mmol/m2 X min, P = 0.09). The decrease in insulin sensitivity was not sufficient to alter glucose tolerance either in the previous gestational diabetic women nor in the nondiabetic women.     

The relationship between first-phase insulin secretion and glucose metabolism.

A possible pathogenetic link between absence of first-phase insulin secretion and development of impaired glucose metabolism has been suggested by the results of several cross-sectional studies. First-phase insulin secretion measured during a +7 mmol/l hyperglycemic glucose clamp correlated with total glucose disposal during the clamp (r = 0.65, p < 0.001, N = 59). To examine whether restoration of first-phase insulin secretion improves peripheral glucose uptake in subjects with impaired glucose utilization, seven insulin-resistant subjects (age 54 (38-62) years: BMI 29.3 (21.7-35.8); fasting plasma glucose 5.5 (4.8-7.2) mmol/l; fasting insulin 57 (37-105) pmol/l with impaired first-phase (148 (29-587) vs controls 485 (326-1086) pmol/l x 10 min; p < 0.05) and normal second-phase (1604 (777-4480) vs controls (1799 (763-2771) pmol/l x 110 min) insulin secretion were restudied. The impaired first-phase insulin secretion was restored by an iv insulin bolus at the start of the hyperglycemic clamp. Substrate oxidation rates and hepatic glucose production were determined by indirect calorimetry and [3-3H]glucose infusion. Total glucose uptake was impaired in the insulin-resistant subjects with impaired first-phase insulin secretion compared to controls (18.8 (13.2-22.2) vs 34.8 (24.3-62.1) mumol.kg-1 x min-1; p < 0.01). Restoration of first-phase insulin secretion (1467 (746-2440) pmol/l x 10 min) did not affect glucose uptake (20.2 (9.9-23.8) mumol.kg-1.min-1), with no difference in oxidative and non-oxidative glucose metabolism between the experiments. Second-phase insulin secretion was similar during both experiments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Association of muscle glycogen synthase polymorphism with insulin resistance in type 2 diabetic patients

The aim of the present study is to investigate whether Met416Val (M416V) polymorphism of glycogen synthase (GYS1) gene is associated with insulin resistance in type 2 diabetes. In 100 type 2 diabetic subjects (66 men and 34 women), the M416V polymorphism of GYS1 gene was analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) as previously reported, and insulin resistance was assessed by euglycemic hyperinsulinemic clamp represented as M/I value, the mean of glucose infusion rate (M value) adjusted by steady state plasma insulin level. The means of age and body mass index (BMI) of the subjects were 53.1+/-11.6 (SD) years and 23.3+/-3.5 kg/m2. The allele frequencies of M416V polymorphism were 82.0% for MM, 16.0% for MV, and 2.0% for VV, and subjects were subsequently divided into V(+) group (n=18) and V(-) group (n=82) according to the presence or absence of V allele. There were no significant differences in age, BMI, blood pressure, fasting plasma glucose or insulin levels or glycosylated hemoglobin (HbA1c) levels between the V(+) and V(-) groups. No significant differences in either M or M/I value were found between the V(+) and V(-) groups (M value, 5.06+/-2.20 v 5.12+/-2.04 mg x kg(-1) x min(-1), P=.841; M/I value, 5.24+/-3.07 v 5.39+/-2.87 mg x kg(-1) x min(-1) x mU(-1) x L, P=.576). BMI showed the strongest independent contribution to M/I value, but the presence of V allele did not in multiple regression analysis. In conclusion, the M416V polymorphism of GYS1 gene is not associated with insulin resistance in type 2 diabetes.     

Changes in plasma growth hormone in diabetic and nondiabetic subjects during the glucose clamp

A group of 22 newly diagnosed noninsulin-dependent diabetic subjects and seven nondiabetic subjects underwent a glucose clamp at plasma glucose 100 mg/dL with insulin infusion rates of 1.0 and 10 mU/kg/min. During both insulin infusion rates, there was a sustained rise in plasma growth hormone (GH) above basal in 18 of the 22 diabetic subjects. Basal GH values were 2.37 +/- 0.67 ng/mL, rising above basal during the lower insulin infusion (6.1 +/- 3.3 ng/mL, P = 0.05) with a further rise at the higher insulin level (8.58 +/- 2.0 ng/mL, P less than 0.001). There was no rise in GH in any of the nondiabetic subjects. In neither group was there any rise above basal in cortisol, prolactin, glucagon, or somatostatin (SRIH). In a group of three nondiabetic subjects, a rise in GH similar to that seen in the diabetic group was induced by elevating the plasma glucose to 200 mg/dL for 60 minutes prior to the euglycemic clamp procedure. However, it is unlikely that changes in plasma glucose account totally for the changes in plasma GH described in the diabetic subjects since a rise in plasma GH was also seen in four diabetic subjects clamped at their fasting plasma glucose. We conclude that in newly diagnosed noninsulin-dependent diabetic subjects there is a rise in plasma GH during the euglycemic clamp procedure, which may be due to both the prior lowering of plasma glucose and the high plasma insulin levels.     

Rats that are made insulin resistant by glucosamine treatment have impaired skeletal muscle insulin receptor phosphorylation

The current study sought to verify whether glucosamine (GlcN)-induced insulin resistance is associated with impaired insulin receptor (IR) autophosphorylation. Rats were given either saline or primed continuous GlcN infusion (5 micromol x kg(-1) x min(-1)) 10 minutes prior to and during euglycemic hyperinsulinemic clamp (primed continuous infusion of 20 mU x kg(-1) x min(-1) insulin for 2 hours). IR autophosphorylation was measured in skeletal muscle after in vivo insulin stimulation (ie, during clamp) by Western blot and then retested after subsequent in vitro 0.1 to 100 nmol/L insulin stimulation (by enzyme-linked immunosorbent assay [ELISA]). Tissue PC-1 enzymatic activity was also measured. In vivo, insulin/GlcN rats had decreased (P <.01) whole body glucose uptake (37.7 +/- 2.1 v 49.7 +/- 2.7 mg x kg(-1) x min(-1) in respect to insulin/saline), receptor autophosphorylation (37 +/- 5 v 82 +/-.0 arbitrary units/mg protein), and insulin receptor substrate-1 (IRS-1) phosphorylation (112% +/- 15% v 198% +/- 23% of saline infusion rats). Receptor autophosphorylation was correlated with whole body glucose uptake (r = 0.62, P <.05). Skeletal muscle PC-1 activity (58.8 +/- 10.7 v 55.7 +/- 5.8 nmol x mg(-1) x min(-1)) was not different in the 2 groups. Our data show that GlcN-induced insulin resistance is mediated, at least in part, by impaired skeletal muscle IR autophosphorylation.     

Effect of pioglitazone on abdominal fat distribution and insulin sensitivity in type 2 diabetic patients

We examined the effect of pioglitazone on abdominal fat distribution to elucidate the mechanisms via which pioglitazone improves insulin resistance in patients with type 2 diabetes mellitus. Thirteen type 2 diabetic patients (nine men and four women; age, 52 +/- 3 yr; body mass index, 29.0 +/- 1.1 kg/m(2)), who were being treated with a stable dose of sulfonylurea (n = 7) or with diet alone (n = 6), received pioglitazone (45 mg/d) for 16 wk. Before and after pioglitazone treatment, subjects underwent a 75-g oral glucose tolerance test (OGTT) and two-step euglycemic insulin clamp (insulin infusion rates, 40 and 160 mU/m(2).min) with [(3)H]glucose. Abdominal fat distribution was evaluated using magnetic resonance imaging at L4-5. After 16 wk of pioglitazone treatment, fasting plasma glucose (179 +/- 10 to 140 +/- 10 mg/dl; P < 0.01), mean plasma glucose during OGTT (295 +/- 13 to 233 +/- 14 mg/dl; P < 0.01), and hemoglobin A(1c) (8.6 +/- 0.4% to 7.2 +/- 0.5%; P < 0.01) decreased without a change in fasting or post-OGTT insulin levels. Fasting plasma FFA (674 +/- 38 to 569 +/- 31 microEq/liter; P < 0.05) and mean plasma FFA (539 +/- 20 to 396 +/- 29 microEq/liter; P < 0.01) during OGTT decreased after pioglitazone. In the postabsorptive state, hepatic insulin resistance [basal endogenous glucose production (EGP) x basal plasma insulin concentration] decreased from 41 +/- 7 to 25 +/- 3 mg/kg fat-free mass (FFM).min x microU/ml; P < 0.05) and suppression of EGP during the first insulin clamp step (1.1 +/- 0.1 to 0.6 +/- 0.2 mg/kg FFM.min; P < 0.05) improved after pioglitazone treatment. The total body glucose MCR during the first and second insulin clamp steps increased after pioglitazone treatment [first MCR, 3.5 +/- 0.5 to 4.4 +/- 0.4 ml/kg FFM.min (P < 0.05); second MCR, 8.7 +/- 1.0 to 11.3 +/- 1.1 ml/kg FFM(.)min (P < 0.01)]. The improvement in hepatic and peripheral tissue insulin sensitivity occurred despite increases in body weight (82 +/- 4 to 85 +/- 4 kg; P < 0.05) and fat mass (27 +/- 2 to 30 +/- 3 kg; P < 0.05). After pioglitazone treatment, sc fat area at L4-5 (301 +/- 44 to 342 +/- 44 cm(2); P < 0.01) increased, whereas visceral fat area at L4-5 (144 +/- 13 to 131 +/- 16 cm(2); P < 0.05) and the ratio of visceral to sc fat (0.59 +/- 0.08 to 0.44 +/- 0.06; P < 0.01) decreased. In the postabsorptive state hepatic insulin resistance (basal EGP x basal immunoreactive insulin) correlated positively with visceral fat area (r = 0.55; P < 0.01). The glucose MCRs during the first (r = -0.45; P < 0.05) and second (r = -0.44; P < 0.05) insulin clamp steps were negatively correlated with the visceral fat area. These results demonstrate that a shift of fat distribution from visceral to sc adipose depots after pioglitazone treatment is associated with improvements in hepatic and peripheral tissue sensitivity to insulin.