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R A DeFronzo

Publications and source records attributed to R A DeFronzo.

At least 37 records · Page 2Linked to original sources
PubMed1999

Synergistic interaction of magnesium and vanadate on glucose metabolism in diabetic rats.

The effect of vanadate (V) alone, magnesium (Mg) alone, and the combination of Mg plus V (MgV) on insulin-mediated glucose disposal and glucose tolerance was investigated in normal and streptozotocin-induced diabetic rats. MgV, magnesium sulfate (MgSO4) and sodium metavanadate (NaV) were added to the drinking water of normal or diabetic rats (approximately 300 g) for 3 weeks. After 3 weeks of V treatment (both MgV and NaV), diabetic rats demonstrated a normal meal tolerance test without any increase in the plasma insulin response. Rats also received a euglycemic insulin clamp (12 mU/kg x min for 120 minutes) with 3-3H-glucose infusion to quantify total body glucose disposal, glycolysis (3H2O production), and glycogen synthesis (total body glucose disposal minus glycolysis). Total glucose disposal was decreased in diabetic versus control rats (29 +/- 2 v 35 +/- 2 mg/kg x min, P < .01) and returned to levels greater than the nondiabetic control values after MgV (41 +/- 2, P < .01). Supersensitivity to insulin was not observed in diabetic rats treated with NaV (34 +/- 1). Glycogen synthesis was increased by both MgV and NaV treatment (23 +/- 21, P < .01 and 18 +/- 1, P < .05 v 14 +/- 2 mg/kg x min) in diabetic rats. A small increase in glycolysis was observed in MgSO4 and MgV rats (18 +/- 1 and 18 +/- 1 v 16 +/- 1, P < .05). NaV alone had no effect on glycolysis. Thus, Mg has a synergistic effect with V to increase muscle glycogen synthesis in diabetic rats. In normal rats, neither MgSO4 nor NaV had any effect on glucose utilization. However, MgV increased glucose disposal to rates that were significantly higher than the rate in untreated control rats (P < .05). Based on these results, MgV is superior to either V alone or Mg alone in improving insulin sensitivity and glycogen synthesis in diabetic rats.

Animals↗
PubMed1999

Urinary platelet-activating factor excretion is elevated in non-insulin dependent diabetes mellitus.

Proteinuria is currently considered a very sensitive predictor of diabetic nephropathy, but 20-25% of all diabetic patients with negative Albustix reaction excrete higher than normal (< 20 mg/24 h) amounts of albumin in their urine. It is our hypothesis that platelet-activating factor (PAF), a potent glycerophospholipid that acts as a chemical mediator for a wide spectrum of biological activities, including increased vascular permeability, may be produced in significant amounts during periods preceding microalbuminuria. In this study, we compared urinary PAF excretion in Mexican-American subjects who were diagnosed with non-insulin dependent diabetes mellitus (NIDDM) with their healthy control counterparts. The age of the NIDDM subjects (45.9 +/- 2.1 years) was not significantly different from the healthy control group, which was 39.4 +/- 2.7 years (P < 0.0672). The NIDDM subjects (body mass index, 29.9 +/- 1.1 compared to 26.1 +/- 0.9 kg/m2 in healthy controls) were characterized by significantly increased (P < 0.05) fasting plasma glucose (192 +/- 11 vs. 97 +/- 4 mg/dl in healthy controls), fasting insulin (20.9 +/- 2.4 vs. 12.3 +/- 1.6 microU/ml), fasting C-peptide (2.93 +/- 1.26 vs. 1.48 +/- 0.51 ng/ml), and hemoglobin A1c (10.3 +/- 0.7 vs. 5.6 +/- 0.3%), respectively. The urine output for the NIDDM and control subjects were 1942 +/- 191 ml/24 h and 1032 +/- 94 ml/24 h, respectively, and urinary albumin excretion (UAE) rates were estimated to be 38 +/- 7 micrograms/min and 11 +/- 1 micrograms/min, respectively. The NIDDM subjects produced significantly increased levels of urinary PAF (2606.3 +/- 513.1 ng/24 h compared with 77.9 +/- 14.1 ng/24 h in controls (or 1706.3 +/- 420.8 ng/ml compared with 85.4 +/- 17.8 pg/ml of urine, in NIDDM and control subjects, respectively). We found that urinary PAF excretion was significantly correlated with microalbumin excretion (r = 0.7) especially at UAE rates greater than 30 mg/day and more importantly, some NIDDM patients with negative Albustix reaction (i.e. normal UAE) produced significantly more PAF, suggesting that PAF excretion may precede microalbuminuria and that subtle injury to the kidneys are present in NIDDM long before overt albuminuria ensues, urinary PAF measurements could potentially therefore serve as a sensitive indicator of renal injury in diabetes mellitus. These results lend further credence to our hypothesis that PAF may be the biochemical compound linking the various members of the insulin resistance syndrome.

Adult↗
PubMed1999

Effects of exercise and insulin on insulin signaling proteins in human skeletal muscle.

Insulin and exercise independently increase glucose metabolism in muscle. Moreover, exercise training or a prior bout of exercise increases insulin-stimulated glucose uptake in resting skeletal muscle. The present study was undertaken to compare how physiological hyperinsulinemia and moderate intensity aerobic exercise affect the tyrosine phosphorylation state and activity of insulin signaling molecules in healthy, physically inactive volunteers. Subjects had biopsies of the vastus lateralis muscle before and immediately after 30 min of either hyperinsulinemia (euglycemic insulin clamp) or moderate-intensity exercise on a cycle ergometer (approximately 60% of VO2max). Insulin receptor and IRS-1 tyrosine phosphorylation, association of the p85 regulatory subunit of PI 3-kinase with IRS-1, IRS-1 associated PI 3-kinase activity, and glycogen synthase activity were determined in muscle biopsy specimens taken from healthy subjects before and after insulin or exercise. Physiological hyperinsulinemia increased the rate of glucose disposal from 11.4 +/- 1.5 to 25.6 +/- 6.7 micromol x kg(-1) x min(-1) (P < 0.01), insulin receptor and IRS-1 tyrosine phosphorylation (173 +/- 19% and 159 +/- 35% of basal values, respectively, P < 0.05), association of the p85 regulatory subunit of PI 3-kinase with IRS-1 (159 +/- 10%, P < 0.05), and glycogen synthase fractional velocity (136 +/- 11%, P < 0.01). Exercise also increased glucose disposal, from 10.4 +/- 0.5 to 15.6 +/- 1.7 micromol x kg(-1) x min(-1) (P < 0.01) and glycogen synthase fractional velocity (253 +/- 35% of basal, P < 0.01). The exercise-induced increase in glycogen synthase was greater than that due to insulin (P < 0.05). In contrast to insulin, exercise decreased tyrosine phosphorylation of the insulin receptor to 72 +/- 10% of basal values (P < 0.05 vs basal and P < 0.05 vs insulin) and had no effect on IRS-1 tyrosine phosphorylation, or association of p85 with IRS-1. The exercise-induced decreased insulin receptor tyrosine phosphorylation could explain the well-known effect of exercise to enhance the sensitivity of muscle to insulin.

Adult↗
PubMed1999

Altered hypothalamic function in response to glucose ingestion in obese humans.

The hypothalamus plays a central role in the regulation of energy intake and feeding behavior. However, the presence of a functional abnormality in the hypothalamus in humans that may be related to excess energy intake and obesity has yet to be demonstrated in vivo. We, therefore, used functional magnetic resonance imaging (fMRI) to monitor hypothalamic function after oral glucose intake. The 10 obese (34 +/- 2 years of age, BMI 34.2 +/- 1.3 kg/m2) and 10 lean (32 +/- 4 years of age, BMI 22.0 +/- 0.9 kg/m2) subjects with normal glucose tolerance ingested 75 g of glucose while a midsagittal slice through the hypothalamus was continuously imaged for 50 min using a conventional T2*-weighted gradient-echo pulse sequence. After glucose ingestion, lean subjects demonstrated an inhibition of the fMRI signal in the areas corresponding to the paraventricular and ventromedial nuclei. In obese subjects, this inhibitory response was markedly attenuated (4.8 +/- 1.3 vs. 7.0 +/- 0.6% inhibition, P < 0.05) and delayed (9.4 +/- 0.5 vs. 6.4 +/- 0.5 min, P < 0.05) compared with that observed in lean subjects. The time taken to reach the maximum inhibitory response correlated with the fasting plasma glucose (r = 0.75, P < 0.001) and insulin (r = 0.47, P < 0.05) concentrations in both lean and obese subjects. These results demonstrate in vivo, for the first time, the existence of differential hypothalamic function in lean and obese humans that may be secondary to obesity.

Adult↗
PubMed1999

Insulin sensitivity indices obtained from oral glucose tolerance testing: comparison with the euglycemic insulin clamp.

OBJECTIVE: Several methods have been proposed to evaluate insulin sensitivity from the data obtained from the oral glucose tolerance test (OGTT). However, the validity of these indices has not been rigorously evaluated by comparing them with the direct measurement of insulin sensitivity obtained with the euglycemic insulin clamp technique. In this study, we compare various insulin sensitivity indices derived from the OGTT with whole-body insulin sensitivity measured by the euglycemic insulin clamp technique. RESEARCH DESIGN AND METHODS: In this study, 153 subjects (66 men and 87 women, aged 18-71 years, BMI 20-65 kg/m2) with varying degrees of glucose tolerance (62 subjects with normal glucose tolerance, 31 subjects with impaired glucose tolerance, and 60 subjects with type 2 diabetes) were studied. After a 10-h overnight fast, all subjects underwent, in random order, a 75-g OGTT and a euglycemic insulin clamp, which was performed with the infusion of [3-3H]glucose. The indices of insulin sensitivity derived from OGTT data and the euglycemic insulin clamp were compared by correlation analysis. RESULTS: The mean plasma glucose concentration divided by the mean plasma insulin concentration during the OGTT displayed no correlation with the rate of whole-body glucose disposal during the euglycemic insulin clamp (r = -0.02, NS). From the OGTT, we developed an index of whole-body insulin sensitivity (10,000/square root of [fasting glucose x fasting insulin] x [mean glucose x mean insulin during OGTT]), which is highly correlated (r = 0.73, P < 0.0001) with the rate of whole-body glucose disposal during the euglycemic insulin clamp. CONCLUSIONS: Previous methods used to derive an index of insulin sensitivity from the OGTT have relied on the ratio of plasma glucose to insulin concentration during the OGTT. Our results demonstrate the limitations of such an approach. We have derived a novel estimate of insulin sensitivity that is simple to calculate and provides a reasonable approximation of whole-body insulin sensitivity from the OGTT.

Administration, Oral↗
PubMed1998

Role of tissue-specific blood flow and tissue recruitment in insulin-mediated glucose uptake of human skeletal muscle.

BACKGROUND: Conflicting evidence exists concerning whether insulin-induced vasodilation plays a mechanistic role in the regulation of limb glucose uptake. It can be predicted that if insulin augments blood flow by causing tissue recruitment, this mechanism would enhance limb glucose uptake. METHODS AND RESULTS: Twenty healthy subjects were studied with the forearm perfusion technique in combination with the euglycemic insulin clamp technique. Ten subjects were studied at physiological insulin concentrations (approximately 400 pmol/L) and the other 10 at supraphysiological insulin concentrations (approximately 5600 pmol/L). Four additional subjects underwent a saline control study. Pulse injections of a nonmetabolizable extracellular marker (1-[3H]-L-glucose) were administered into the brachial artery, and its washout curves were measured in one ipsilateral deep forearm vein and used to estimate the extracellular volume of distribution and hence the amount of muscle tissue drained by the deep forearm vein. Both during saline infusion and at physiological levels of hyperinsulinemia we observed no changes in blood flow and/or muscle tissue drained by the deep forearm vein. However, supraphysiological hyperinsulinemia accelerated total forearm blood flow (45.0+/-1.8 versus 36.5+/-1.3 mL x min(-1) x kg(-1), P<0.01) and increased the amount of muscle tissue drained by the deep forearm vein (305+/-46 versus 229+/-32 g, P<0.05). The amount of tissue newly recruited by insulin was strongly correlated to the concomitant increase in tissue glucose uptake (r=0.789, P<0.01). CONCLUSIONS: Acceleration of forearm blood flow mediated by supraphysiological hyperinsulinemia is accompanied by tissue recruitment, which may be a relevant determinant of forearm (muscle) glucose uptake.

Adult↗
PubMed1998

Neonatal de-afferentation of capsaicin-sensitive sensory nerves increases in vivo insulin sensitivity in conscious adult rats.

Sensory neuropeptides, released from the peripheral nervous system, might modulate glucose homeostasis by antagonizing insulin action. The effects of de-afferentation of functional small diameter unmyelinated C-fibres (sensory nerves) on in vivo insulin-mediated intracellular glucose metabolism were investigated by using euglycaemic insulin (6 and 18 mU/kg x min) clamps with [3-(3)H]-glucose infusion in 24 adult rats, treated neonatally with either capsaicin (CAP) (50 mg/kg) or vehicle (CON). Following the clamp, skeletal muscle groups, liver and adipose tissue were freeze-clamped. At plasma insulin levels of approximately 90 mU/l, CAP-rats showed a 21% increase in whole body glucose uptake compared with CON (24.4 +/- 1.6 vs 20.1 +/- 0.8 mg/kg min, p < 0.02), which was paralleled by a 20% increase in whole body glycolysis (12.6 +/- 0.8 vs 10.5 +/- 0.5 mg/ kg.min p < 0.05) (concentration of 3H2O in plasma). Whole body skeletal muscle glycogenesis was increased by 80% in CAP-rats (5.7 +/- 0.7 vs 3.1 +/- 0.7 mg/kg x min, p < 0.05) with increased muscle glycogen synthase activity. Whole body (muscle, liver and adipose tissue combined) de novo lipogenesis also was increased in CAP-rats compared with CON (0.69 +/- 0.10 vs 0.44 +/- 0.06 mg/kg x min, p < 0.05) (incorporation of [3-(3)H]-glucose counts into glycogen or fat). Hepatic glucose production was lower in CAP-rats compared with CON (0.6 +/- 0.6 vs 2.1 +/- 0.7 mg/kg x min, p < 0.05). Plasma glucagon, corticosterone, epinephrine and norepinephrine levels were reduced in CAP-rats: 43 +/- 2 compared with 70 +/- 6 pg/ml, 855 +/- 55 compared with 1131 +/- 138 nmol/l, 513 +/- 136 compared with 1048 +/- 164 pmol/l and 928 +/- 142 compared with 1472 +/- 331 pmol/l, respectively, p < 0.05. At plasma insulin levels of approximately 400 mU/l, CAP-rats showed no differences in peripheral and hepatic insulin action compared with CON. We conclude that the removal of endogenous sensory neuropeptides, by de-afferentation of capsaicin-sensitive sensory nerves, increases in vivo insulin sensitivity, but not responsiveness: 1) primarily through an increased sensitivity of skeletal muscle glycogen synthesis to insulin; 2) through a reduction in the levels of counter-regulatory hormones, thereby creating a milieu which favours overall in vivo insulin sensitivity with respect to glucose uptake, glucose production, glycolysis, glycogenesis and lipogenesis.

Afferent Pathways↗
PubMed1998

Regulation of hexokinase II activity and expression in human muscle by moderate exercise.

A single bout of exercise increases the rate of insulin-stimulated glucose uptake and metabolism in skeletal muscle. Exercise also increases insulin-stimulated glucose 6-phosphate in skeletal muscle, suggesting that exercise increases hexokinase activity. Within 3 h, exercise increases hexokinase II (HK II) mRNA and activity in skeletal muscle from rats. It is not known, however, if a single bout of moderate-intensity exercise increases HK II expression in humans. The present study was undertaken to answer this question. Six subjects had percutaneous biopsies of the vastus lateralis muscle before and 3 h after a single 3-h session of moderate-intensity aerobic (60% of maximal oxygen consumption) exercise. Glycogen synthase, HK I, and HK II activities as well as HK I and HK II mRNA content were determined from the muscle biopsy specimens. The fractional velocity of glycogen synthase was increased by 446 +/- 84% after exercise (P < 0.005). Hexokinase II activity in the soluble fraction of the homogenates increased from 1.2 +/- 0.4 to 4.5 +/- 1.6 pmol.min-1.microgram-1 (P < 0.05) but was unchanged in the particulate fraction (4.3 +/- 1.3 vs. 5.3 +/- 1.5). HK I activity in neither the soluble nor particulate fraction changed after exercise. Relative to a 28S rRNA control signal, HK II mRNA increased from 0.091 +/- 0.02 to 0.195 +/- 0.037 (P < 0.05), whereas HK I mRNA was unchanged (0.414 +/- 0.061 vs. 0.498 +/- 0.134, P < 0.20). The increase in HK II activity after moderate exercise in healthy subjects could be one factor responsible for the enhanced rate of insulin-stimulated glucose uptake seen after exercise.

Adult↗
PubMed1998

Time course of insulin action on tissue-specific intracellular glucose metabolism in normal rats.

We investigated the time course of insulin action in conscious rats exposed to constant physiological hyperinsulinemia (approximately 100 mU/l) while maintaining euglycemia (approximately 100 mg/dl) for 0, 0.5, 2, 4, 8, or 12 h. [3-3H]glucose was infused to quantitate whole body glucose disposal (rate of disappearance, Rd), glycolysis (generation of 3H2O in plasma), hepatic glucoses production (HGP), and skeletal muscle and liver glycogen synthesis ([3-3H]glucose incorporation into glycogen and time-dependent change in tissue glycogen concentration). The basal Rd, which equals HGP, was 6.0 +/- 0.3 mg.kg-1.min-1. With increased duration of hyperinsulinemia from 0 to 0.5 to 2 to 4 h, Rd increased from 6.0 +/- 0.3 to 21.0 +/- 1.1 to 24.1 +/- 1.5 to 26.6 +/- 0.6 mg.kg-1.min-1 (P < 0.05 for 2 and 4 h vs. 0.5 h). During the first 2 h the increase in Rd was explained by parallel increases in glycolysis and glycogen synthesis. From 2 to 4 h the further increase in Rd was entirely due to an increase in glycolysis without change in glycogen synthesis. From 4 to 8 to 12 h of hyperinsulinemia, Rd decreased by 19% from 26.6 +/- 0.6 to 24.1 +/- 1.1 to 21.6 +/- 1.8 mg.kg-1.min-1 (P < 0.05 for 8 h vs. 4 h and 12 h vs. 8 h). The progressive decline in Rd, in the face of constant hyperinsulinemia, occurred despite a slight increase (8-14%) in glycolysis and was completely explained by a marked decrease (64%) in muscle glycogen synthesis. In contrast, liver glycogen synthesis increased fourfold, indicating an independent regulation of muscle and liver glycogen synthesis by long-term hyperinsulinemia. In the liver, during the entire 12-h period of insulin stimulation, the contribution of the direct (from glucose) and the indirect (from C-3 fragments) pathways to net glycogen formation remained constant at 77 +/- 5 and 23 +/- 5%, respectively. HGP remained suppressed throughout the 12-h period of hyperinsulinemia.

Adipose Tissue↗
PubMed1998

Effect of hyperinsulinemia on plasma leptin concentrations and food intake in rats.

We investigated the dose- and time-dependent effect of insulin infusion on peripheral and portal plasma leptin concentrations in normal rats. Three groups were studied: group I: euglycemic (6 mmol/l) insulin (6 mU . kg-1 . min-1) clamps for 0, 2, 4, 12, and 24 h; group II: euglycemic insulin (18 mU . kg-1 . min-1) clamp for 2 h; and group III: euglycemic insulin (3 mU . kg-1 . min-1) clamp for 7 days. In group III, food intake was quantified during days 1-7. After an overnight fast, peripheral and portal plasma leptin levels were identical (1.5 +/- 0.2 and 1.6 +/- 0.2 ng/ml). Insulin infusion (6 mU . kg-1 . min-1) for 2 h had no effect on plasma leptin levels (1.5 +/- 0.2 ng/ml). After 4 h (2.0 +/- 0.2 ng/ml), 12 h (2.2 +/- 0. 4 ng/ml), and 24 h (2.7 +/- 0.6 ng/ml; all P < 0.05) of insulin infusion, a progressive time-related increase in plasma leptin concentration was observed; portal vein leptin levels rose in parallel and were similar to peripheral levels. When insulin (18 mU . kg-1 . min-1) was infused for 2 h, plasma leptin levels increased to 3.0 +/- 0.3 ng/ml (P < 0.01). Seven days of constant insulin infusion (3 mU . kg-1 . min-1) resulted in a progressive increase in fasting plasma leptin and a parallel decrease in food intake. A mean increase in plasma leptin concentration of 1 ng/ml during the 7-day insulin infusion period was associated with a mean decrease in food intake of 2.5 g/day (multivariate ANOVA, P < 0.05). We conclude that the insulin-induced rise in peripheral and portal vein leptin levels is similar and both dose and time dependent. The inverse relationship between plasma leptin concentration and food intake during prolonged hyperinsulinemia, but not during short-term hyperinsulinemia, supports the role of leptin in long-term food consumption.

Animals↗
PubMed1998

IGF-I increases forearm blood flow without increasing forearm glucose uptake.

Decreased insulin-mediated muscle glucose uptake is a characteristic feature of non-insulin-dependent diabetes mellitus and other insulin-resistant states. It has been suggested that an impairment in the ability of insulin to augment limb blood flow, resulting in diminished glucose delivery to muscle, may contribute to this abnormality. In this study, we used human insulin-like growth factor (IGF) I in conjunction with the forearm balance technique to determine whether forearm glucose uptake could be stimulated by increasing blood flow without directly stimulating the intrinsic ability of the muscle to extract glucose. IGF-I was infused intra-arterially in healthy controls at a rate of either 0.4 microg . kg-1 . min-1 (high IGF) or 0.04 microg . kg-1 . min-1 (low IGF) for 140 min. With high IGF, forearm blood flow increased approximately twofold (34 +/- 3 vs. 64 +/- 8 ml . min-1 . l forearm volume-1, P < 0.01), and arteriovenous glucose concentration difference (a-v difference) increased modestly (0.19 +/- 0.05 vs. 0.31 +/- 0.08 mM, P = 0.32), resulting in an increased forearm glucose uptake (6.4 +/- 1.7 vs. 21.7 +/- 7.4 micromol . min-1 . l forearm volume-1, P = 0.09 vs. basal). With low IGF, forearm blood flow increased by 59% (29 +/- 4 vs. 46 +/- 9 ml . min-1 . l forearm volume-1, P < 0.05) and was associated with a proportional decrease in the a-v difference (0. 29 +/- 0.04 vs. 0.18 +/- 0.05 mM, P < 0.05). Forearm glucose uptake therefore was not significantly different from basal values (7.6 +/- 0.6 vs. 6.9 +/- 1.8 micromol . min-1 . kg-1). These data demonstrate that increasing blood flow without increasing the intrinsic ability of the muscle to extract glucose does not increase forearm muscle glucose uptake.

Adult↗
PubMed1998

Insulin-induced hexokinase II expression is reduced in obesity and NIDDM.

NIDDM and obesity are characterized by decreased insulin-stimulated glucose uptake in muscle. It has been suggested that impaired glucose phosphorylation to glucose-6-phosphate, catalyzed in muscle by hexokinase (HK)II, may contribute to this insulin resistance. Insulin is known to increase HKII mRNA, protein, and activity in lean nondiabetic individuals. The purpose of this study was to determine whether defects in insulin-stimulated HKII expression and activity could contribute to the insulin resistance of obesity and NIDDM. Fifteen lean nondiabetic control subjects, 17 obese nondiabetic subjects, and 14 obese NIDDM patients were studied. Percutaneous muscle biopsies of the vastus lateralis were performed in conjunction with leg balance and local indirect calorimetry measurements before and at the end of a 3-h euglycemic-hyperinsulinemic clamp (40 or 240 mU x min(-1) x m[-2]). Leg glucose uptake in response to the 40-mU insulin infusion was higher in the lean control subjects (2.53 +/- 0.35 micromol x min(-1) per x 100 ml leg vol) than in obese (1.46 +/- 0.50) or NIDDM (0.53 +/- 0.25, P < 0.05) patients. In response to 240 mU insulin, leg glucose uptake was similar in all of the groups. In response to 40 mU insulin, HKII mRNA in lean control subjects was increased 1.48 +/- 0.18-fold (P < 0.05) but failed to increase significantly in the obese (1.12 +/- 0.24) or NIDDM (1.14 +/- 0.18) groups. In response to 240 mU insulin, HKII mRNA was increased in all groups (control subjects 1.48 +/- 0.18, P < 0.05 vs. basal, obese 1.30 +/- 0.16, P < 0.05, and NIDDM 1.25 +/- 0.14, P < 0.05). Under basal conditions, HKI and HKII activities did not differ significantly between groups. Neither the 40 mU nor the 240 mU insulin infusion affected HK activity. Total HKII activity was reduced in the obese subjects (4.33 +/- 0.08 pmol x min(-1) x g(-1) muscle protein) relative to the lean control subjects (5.00 +/- 0.08, P < 0.05). There was a further reduction in the diabetic patients (3.10 +/- 0.10, P < 0.01 vs. the control subjects, P < 0.01 vs. the obese subjects). Resistance to insulin's metabolic effects extends to its ability to induce HKII expression in obesity and NIDDM.

Adult↗
PubMed1997

In vitro and in vivo suppression of gluconeogenesis by inhibition of pyruvate carboxylase.

The mechanism of inhibition of gluconeogenesis by phenylalkanoic acids was studied in vitro and in vivo. In vitro production of 14CO2 from labeled glucose or palmitate was not inhibited at 4 mM, a concentration of phenylacetic acid that inhibited gluconeogenesis from lactate/pyruvate. In vitro studies with isolated mitochondria showed that the CoA ester of phenylacetic acid was formed. The parent phenylalkanoic acid had no effect on purified pyruvate carboxylase activity, but phenylacetyl CoA ester decreased pyruvate carboxylation in a concentration-dependent manner. Phenylacetic acid inhibited gluconeogenesis in isolated rat liver cells from 10 mM lactate/1 mM pyruvate (decreased 39%, P < 0.05), but not 10 mM L-glutamine or [14C]aspartate, showing that the inhibition of gluconeogenesis occurred at the level of pyruvate carboxylase. A 20 mg bolus with infusion of 1 mg/min of phenylpropionic acid decreased blood glucose levels of normal [110 +/- 12 to 66 +/- 11 mg/dL, N = 7, P < 0.05 (unpaired Student's t-test vs control)] and streptozocin diabetic rats [295 +/- 14 to 225 +/- 12 mg/dL, N = 7, P < 0.01 (paired t-test vs basal)]. Hepatic glucose production in control and diabetic rats was suppressed under conditions where liver glycogen was depleted, indicating that gluconeogenesis had been inhibited in vivo. The results suggest the possibility that the inappropriate overproduction of glucose can be controlled by inhibitors of pyruvate carboxylase. This class of inhibitors may be useful in the treatment of non-insulin-dependent diabetes mellitus.

Animals↗
PubMed1997

UDP-N-acetylglucosamine transferase and glutamine: fructose 6-phosphate amidotransferase activities in insulin-sensitive tissues.

Glutamine:fructose 6-phosphate amidotransferase (GFA) is rate-limiting for hexosamine biosynthesis, while a UDP-GlcNAc beta-N-acetylglucosaminyltransferase (O-GlcNAc transferase) catalyses final O-linked attachment of GlcNAc to serine and threonine residues on intracellular proteins. Increased activity of the hexosamine pathway is a putative mediator of glucose-induced insulin resistance but the mechanisms are unclear. We determined whether O-GlcNAc transferase is found in insulin-sensitive tissues and compared its activity to that of GFA in rat tissues. We also determined whether non-insulin-dependent diabetes mellitus (NIDDM) or acute hyperinsulinaemia alters O-GlcNAc transferase activity in human skeletal muscle. O-GlcNAc transferase was measured using 3H-UDP-GlcNAc and a synthetic cationic peptide substrate containing serine and threonine residues, and GFA was determined by measuring a fluorescent derivative of GlcN6P by HPLC. O-GlcNAc transferase activities were 2-4 fold higher in skeletal muscles and the heart than in the liver, which had the lowest activity, while GFA activity was 14-36-fold higher in submandibular gland and 5-18 fold higher in the liver than in skeletal muscles or the heart. In patients with NIDDM (n = 11), basal O-GlcNAc transferase in skeletal muscle averaged 3.8 +/- 0.3 nmol/mg.min, which was not different from that in normal subjects (3.3 +/- 0.4 nmol/mg.min). A 180-min intravenous insulin infusion (40 mU/m2.min) did not change muscle O-GlcNAc transferase activity in either group. We conclude that O-GlcNAc transferase is widely distributed in insulin-sensitive tissues in the rat and is also found in human skeletal muscle. These findings suggest the possibility that O-linked glycosylation of intracellular proteins is involved in mediating glucose toxicity. O-GlcNAc transferase does not, however, appear to be regulated by either NIDDM or acute hyperinsulinaemia, suggesting that mass action effects determine the extent of O-linked glycosylation under hyperglycaemic conditions.

Adipose Tissue↗
PubMed1997

Studies on the mass action effect of glucose in NIDDM and IDDM: evidence for glucose resistance.

UNLABELLED: The ability of hyperglycaemia to enhance glucose uptake was evaluated in 9 non-insulin-dependent (NIDDM), 7 insulin-dependent (IDDM) diabetic subjects, and in 6 young and 9 older normal volunteers. Following overnight insulin-induced euglycaemia, a sequential three-step hyperglycaemic clamp (+ 2.8 + 5.6, and + 11.2 mmol/l above baseline) was performed with somatostatin plus replacing doses of basal insulin and glucagon, 3-3H-glucose infusion and indirect calorimetry. In the control subjects as a whole, glucose disposal increased at each hyperglycaemic step (13.1 +/- 0.6, 15.7 +/- 0.7, and 26.3 +/- 1.1 mumol/kg.min). In NIDDM (10.5 +/- 0.2, 12.1 +/- 1.0, and 17.5 +/- 1.1 mumol/kg.min), and IDDM (11.2 +/- 0.8, 12.9 +/- 1.0, and 15.6 +/- 1.1 mumol/kg.min) glucose disposal was lower during all three steps (p < 0.05-0.005). Hepatic glucose production declined proportionally to plasma glucose concentration to a similar extent in all four groups of patients. In control subjects, hyperglycaemia stimulated glucose oxidation (+4.4 +/- 0.7 mumol/kg.min) only at +11.2 mmol/l (p < 0.05), while non-oxidative glucose metabolism increased at each hyperglycaemic step (+3.1 +/- 0.7; +3.5 +/- 0.9, and +10.8 +/- 1.7 mumol/kg.min; all p < 0.05). In diabetic patients, no increment in glucose oxidation was elicited even at the highest hyperglycaemic plateau (IDDM = +0.5 +/- 1.5; NIDDM = +0.2 +/- 0.6 mumol/kg.min) and non-oxidative glucose metabolism was hampered (IDDM = +1.8 +/- 1.5, +3.1 +/- 1.7, and +4.3 +/- 1.8; NIDDM = +0.7 +/- 0.6, 2.1 +/- 0.9, and +7.0 +/- 0.8 mumol/kg.min; p < 0.05-0.005). Blood lactate concentration increased and plasma non-esterified fatty acid (NEFA) fell in control (p < 0.05) but not in diabetic subjects. The increments in blood lactate were correlated with the increase in non-oxidative glucose disposal and with the decrease in plasma NEFA. IN CONCLUSION: 1) the ability of hyperglycaemia to promote glucose disposal is impaired in NIDDM and IDDM; 2) stimulation of glucose oxidation and non-oxidative glucose metabolism accounts for glucose disposal; 3) both pathways of glucose metabolism are impaired in diabetic patients; 4) impaired ability of hyperglycaemia to suppress plasma NEFA is present in these patients. These results suggest that glucose resistance, that is the ability of glucose itself to promote glucose utilization, is impaired in both IDDM and NIDDM patients.

Adult↗
PubMed1997

Hyperamylinemia is associated with hyperinsulinemia in the glucose-tolerant, insulin-resistant offspring of two Mexican-American non-insulin-dependent diabetic parents.

Several investigations have presented evidence that amylin inhibits insulin secretion and induces insulin resistance both in vitro and in vivo. However, basal and postmeal amylin concentrations proved similar in non-insulin-dependent diabetes mellitus (NIDDM) patients and controls. Since hyperglycemia may alter both amylin and insulin secretion, we examined basal and glucose-stimulated amylin secretion in eight glucose-tolerant, insulin-resistant Mexican-American subjects with both parents affected with NIDDM (offspring) and correlated the findings with the insulin sensitivity data acquired by an insulin clamp. Eight offspring and eight Mexican-Americans without any family history of diabetes (controls) underwent measurement of fat free mass (3H2O dilution method), 180-minutes, 75-g oral glucose tolerance test (OGTT), and 40-mU/m2, 180-minute euglycemic insulin clamp associated with 3H-glucose infusion and indirect calorimetry. Fasting amylin was significantly increased in offspring versus controls (11.5 +/- 1.4 v 7.0 +/- 0.8 pmol/L, P < .05). After glucose ingestion, both total (3,073 +/- 257 v 1,870 +/- 202 pmol.L-1.min-1, P < .01) and incremental (1,075 +/- 170 v 518 +/- 124 pmol.L-1.min-1, P < .05) areas under the curve (AUCs) of amylin concentration were significantly greater in offspring. The amylin to insulin molar ratio was similar in offspring and controls at all time points. Basal and postglucose insulin and C-peptide concentrations were significantly increased in the offspring. No correlation was found between fasting amylin, postglucose amylin AUC or IAUC, and any measured parameter of glucose metabolism during a euglycemic-hyperinsulinemic clamp (total glucose disposal, 7.21 +/- 0.73 v 11.03 +/- 0.54, P < .001; nonoxidative glucose disposal, 3.17 +/- 0.59 v 6.33 +/- 0.56, P < .002; glucose oxidation, 4.05 +/- 0.46 v 4.71 +/- 0.21, P = NS; hepatic glucose production, 0.29 +/- 0.16 v 0.01 +/- 0.11, P = NS; all mg.min-1.kg-1 fat-free mass, offspring v controls). In conclusion, these data do not support a causal role for amylin in the genesis of insulin resistance in NIDDM.

Adult↗
PubMed1997

Na+/Li+ and Na+/H+ countertransport activity in hypertensive non-insulin-dependent diabetic patients: role of insulin resistance and antihypertensive treatment.

We measured erythrocyte Na+/Li+ and Na+/H+ countertransport (CT) activity (millimoles per liter per cell per hour) in 10 healthy control subjects (age, 38 +/- 4 years; body mass index, 25 +/- 1 kg/m2) and in 25 hypertensive patients with non-insulin-dependent diabetes mellitus ([NIDDM] age, 49 +/- 3 years; body mass index, 29 +/- 1 kg/m2; fasting plasma glucose, 157 +/- 12 mg/dL) 4 weeks after discontinuation of previous antihypertensive treatment. Na+/Li+ CT was significantly increased in hypertensive NIDDM patients compared with controls (0.56 +/- 0.04 v 0.30 +/- 0.03, P < .01), whereas Na+/H+ CT was similar to control levels (21 +/- 1 v 20 +/- 2). A positive correlation was found between Na+/Li+ CT and the severity of insulin resistance (r = .69, P < .01), mean arterial pressure ([MAP] r = .64, P < .01), plasma triglyceride concentration (r = .46, P < .05), and plasma total cholesterol (r = .41, P < .05). An inverse correlation was found between Na+/Li+ CT activity and plasma insulin concentration (r = -.47, P < .05). No relationship was observed between Na+/Li+ CT activity and either creatinine clearance or proteinuria. Stepwise multiple regression analysis for all metabolic variables and blood pressure showed that only the severity of insulin resistance was positively correlated with increased Na+/Li+ CT activity. Na+/H+ and Na+/Li+ CT activity were not altered by 3 hours of euglycemic physiologic hyperinsulinemia (84 +/- 3 microU/mL). Hypertensive NIDDM subjects were treated for 3 months with captopril, nifedipine, or doxazosin. After captopril, a reduction of Na+/H+ CT was observed (22 +/- 4 v 13 +/- 2, P < .05); Na+/Li+ CT decreased after doxazosin (0.56 +/- 0.06 v 0.45 +/- 0.05, P < .05) and nifedipine (0.52 +/- 0.06 v 0.42 +/- 0.05, P < .05). In conclusion, in hypertensive NIDDM subjects, (1) Na+/Li+ CT is increased and is correlated with the level of insulin resistance and the MAP; (2) acute physiologic hyperinsulinemia does not affect Na+/Li+ or Na+/H+ CT activity; and (3) Na+/H+ CT activity is reduced by captopril, and Na+/Li+ CT is decreased by doxazosin and nifedipine.

Adult↗