Insulin Binding In Adipocytes Research Articles

Effects of peroxovanadate and vanadate on insulin binding, degradation and sensitivity in rat adipocytes

The effects of vanadate and the stable peroxovanadate compound bpV(pic) on insulin binding and degradation were investigated in rat adipocytes under conditions of ongoing receptor cycling. Both bpV(pic) and vanadate increased 125I-insulin binding to intact cells through an increase in apparent receptor affinity. The maximal effect of bpV(pic) was to increase binding ∼4-fold (EC 50 0.06 ± 0.01 mM), whereas vanadate increased binding ∼2-fold (EC 50 1.4 ± 0.2 mM). Removal of cell surface insulin-receptor complexes with trypsin showed that the effects on binding exerted by bpV(pic) and vanadate were due to a similar increase in both cell surface binding and intracellular accumulation of radioactivity. Both bpV(pic) and vanadate inhibited the degradation of 125I-insulin in medium containing 1% bovine serum albumin. The ratio of degraded/intact intracellular 125I-insulin was also markedly reduced by these agents, suggesting that they inhibit intracellular insulin-degrading proteases. Similar to previous findings with vanadate, bpV(pic) stimulated glucose transport and, at low concentrations, enhanced insulin sensitivity. Taken together, these data demonstrate that both bpV(pic) and vanadate inhibit insulin degradation. In addition, they significantly enhance cell surface insulin binding in rat fat cells and this is associated with an improved insulin sensitivity.

Severe impairment of insulin action in adipocytes from amenorrheic subjects with polycystic ovary syndrome

Adipose tissue was used to characterize the metabolic abnormality of insulin resistance in polycystic ovary syndrome (PCOS). Nine patients with PCOS were studied during a period of amenorrhea and confirmed to be chronically anovulatory by vaginal ultrasound and plasma progesterone measurements. These were compared with six age- and body mass index (BMI)-matched controls (BMI, 27.2 ± 2.2 in PCOS and 24.7 ± 2.3 in control subjects). Insulin receptor binding was measured and insulin action was assessed by measuring initial rates of 3- O-methylglucose uptake and by inhibition of lipolysis. The maximum specific insulin receptor binding was 0.62% ± 0.12% and 1.78% ± 0.18% per 10-cm 2 cell surface (mean ± SEM) in PCOS and control subjects, respectively ( P < .001). Maximum rates of glucose transport were also impaired as compared with controls, with 3- O-methylglucose transport being 0.90 ± 0.15 versus 1.57 ± 0.28 pmol/10 cm 2/5s, respectively ( P < .05). The concentration of insulin required for half-maximal stimulation of glucose uptake was 165 ± 36 versus 32 ± 10 pmol in PCOS and control subjects, respectively ( P < .05). The maximum percentage lipolysis inhibition (mean ± SEM) was 9.5% ± 1.6% in PCOS and 28.3% ± 7.2% in control patients, respectively ( P < .01). These data demonstrate that there are both insulin binding and postreceptor defects in adipocytes from amenorrheic PCOS subjects. The degree of defect in adipocyte insulin action is greater than would have been anticipated from in vivo data.

Evidence for Distinctive and Intrinsic Defects in Insulin Action in Polycystic Ovary Syndrome

Women with PCO have a unique but poorly characterized disorder of insulin action. Obese (n = 16) and nonobese (n = 14) PCO women and age- and weight-matched normal, nondiabetic ovulatory women (obese, n = 15; nonobese, n = 17) had insulin action determined in vivo with sequential multiple insulin dose euglycemic clamps and in isolated abdominal adipocytes to clarify the mechanisms of insulin resistance. PCO resulted in significant increases in the ED50 insulin for glucose utilization in vivo (P less than 0.001) and in adipocytes (P less than 0.01), without significant changes in adipocyte insulin-binding sites. PCO also resulted in significant decreases in maximal insulin-stimulated rates of glucose utilization in vivo (P less than 0.01) and in adipocytes (P less than 0.01). Obesity resulted in smaller decreases in insulin sensitivity than PCO (ED50 insulin, P less than 0.001 in vivo and P less than 0.05 in adipocytes), but greater decreases in insulin responsiveness (Vmax, P less than 0.001 in vivo and in adipocytes). The ED50 insulin for suppression of HGP was increased only in obese PCO women (P less than 0.001), and the interactions between PCO and obesity on this parameter were statistically significant. No significant correlations between androgen or estrogen levels and adipocyte insulin binding or action were found. Because insulin binding was not changed, we conclude that the major lesion causing insulin resistance in PCO is a striking decrease in insulin sensitivity secondary to a defect in the insulin receptor and/or postreceptor signal transduction. PCO also is associated with modest but significant decreases in glucose transport. These defects in insulin action appear to represent intrinsic abnormalities that are independent of obesity, metabolic derangements, body fat topography, and sex hormone levels. Conversely, changes in hepatic insulin sensitivity appear to be acquired with obesity.

Vanadate increases cell surface insulin binding and improves insulin sensitivity in both normal and insulin-resistant rat adipocytes.

The aim of this study was to elucidate the acute effects of vanadate on cell surface insulin binding and insulin sensitivity in rat adipocytes. The cells were preincubated at 37 degrees for 20 min followed by energy depletion with potassium cyanide, extensive washing and 125I-insulin binding. The presence of vanadate or insulin during the preincubation period dose-dependently enhanced 125I-insulin binding to normal adipocytes (maximally 4-5-fold) through an increased number of binding sites without any change in receptor affinity. Submaximal concentrations of vanadate added together with insulin enhanced the cellular sensitivity to the effect of insulin to stimulate 3-O-methylglucose transport. Vanadate, but not insulin, was also capable of increasing insulin binding as well as insulin sensitivity in insulin-resistant cells (treatment with N6-monobutyryl cAMP or amiloride and adipocytes from obese, aging rats). There was a correlation between the effect of vanadate to augment insulin binding and its ability to enhance cellular insulin sensitivity. Thus, the data suggest that short-term vanadate treatment improves insulin sensitivity through enhanced receptor binding and that this occurs in both normal and insulin-resistant cells.

Effects of interferon alpha on insulin binding and glucose transport in human adipocytes.

We have previously demonstrated that interferon administration impairs glucose tolerance and causes insulin resistance in healthy man. Whether this is a direct effect of interferon is not known. The present study was undertaken to examine directly the effect of interferon alpha on insulin binding and action on glucose transport in isolated human adipocytes. Different concentrations of interferon alpha (range 10(-3)-10(5) IU ml-1) and different incubation times (0-5-24 h) with interferon were employed. Acute and 5-h and 24-h exposure of human adipocytes to 10(-2)-10 IU ml-1 of interferon increased the high affinity binding of 125I-insulin (P less than 0.05). In contrast, human interferon alpha had no effect on insulin binding in rat adipocytes. In short-term studies interferon had no effect on 14C-glucose transport clearance. 24-h preincubation of human adipocytes with 10(-2), 10, 10(4) IU ml-1 interferon increased maximally-insulin stimulated 14C-glucose transport clearance (P less than 0.05) and glucose transport responsiveness to insulin was enhanced by 24% (P less than 0.05) in cells exposed to 10(-2) IU ml-1 interferon. After 5 and 24-h preincubations with interferon we observed modest changes in glucose transport sensitivity to moderate concentrations of insulin (50-100 pM) with upregulation in the presence of 10(-2)-10 IU ml-1 interferon and downregulation in the presence of 10(4)-10(5) IUm ml-1 interferon (P less than 0.05). The insulin sensitivity index (ED50) did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Manganese Deficiency on Insulin Binding, Glucose Transport and Metabolism in Rat Adipocytes

The effect of manganese deficiency on insulin binding, glucose transport and metabolism in isolated adipose cells from Sprague-Dawley rats was investigated. Offspring from Mn-sufficient female rats fed 45 micrograms Mn/g diet (control) and from Mn-deficient (Mn-) female rats fed 1 microgram Mn/g diet were used in these studies. Both basal and insulin-stimulated 3-O-methylglucose transport in isolated adipose cells was significantly lower in Mn- rats, averaging 40% and 50% of control values, respectively. Kinetic analysis of glucose transport demonstrated a lower maximal transport velocity (Vmax) for glucose in adipose cells from Mn- rats compared to controls. No differences in the Km for glucose uptake were observed between the two groups. Insulin-stimulated glucose oxidation to CO2 and conversion to triglycerides was lower in isolated adipose cells from Mn- rats compared to controls. Mn- animals had fewer insulin receptors per cell compared to controls, although no differences in insulin receptor affinity were observed between the two groups. These data suggest that Mn deficiency affects glucose transport and metabolism in the adipose cell. The apparent defect lies distal to the insulin receptor and probably reflects a decreased number of glucose transporters in adipose tissue of Mn- rats.

Effect of prolonged hyperinsulinaemia on adipocyte insulin binding and action in normal man

Prolonged moderate insulinaemia over 20 h in normal humans produces a significant reduction of in vivo insulin action. To examine the effects in man of such moderate hyperinsulinaemia on in vitro glucose metabolism, insulin-receptor binding, glucose transport and incorporation of glucose into lipid were determined in adipocytes isolated from paired gluteal fat biopsies, taken from six normal human volunteers before and 1 h after 20 h of exogenous hyperinsulinaemia (plasma insulin 38 ± 3 mU/l). Specific binding of insulin to isolated adipocytes was not altered (6.7 ± 0.7 versus 7.6 ± 1.5% per 10 5 cells). Basal glucose transport of 3- O-[ 14C]methylglucose in the absence of insulin was reduced after hyperinsulinaemia (5.2 ± 1.1 versus post 4.3 ± 1.3 pmol/7 s per 10 5 cells, 0.1 < P > 0.05; or expressed as percent of maximal response: 60 ± 5 versus post 49 ±1%, P< 0.05), but maximal transport (9.2 ± 1.5 versus post 8.7 ± 1.5 pmol/7 s per 10 5 cells and ED 50 (89 ± 17 versus 67 ± 15 pmol/l) were unchanged. Conversion of glucose into lipid, using 3- d-[ 3H]glucose, was unchanged basally, at maximal response or ED 50 of the dose response curve. In conclusion, moderate 20 h in vivo hyperinsulinaemia in normal humans induces only a small change in basal vitro adipocyte glucose transport, and no change in insulin-receptor binding or in vitro incorporation of glucose into lipid. These data suggest that the adipocyte does not contribute to the impaired insulin action produced by in vivo moderate hyperinsulinaemia in man.

Diet fat composition alters membrane phospholipid composition, insulin binding, and glucose metabolism in adipocytes from control and diabetic animals.

The present study was designed to determine if diet fat-induced alteration in the fatty acid composition of the adipocyte plasma membrane alters insulin binding and the insulin responsiveness of glucose metabolism in control and diabetic states. Normal (control) and diabetic (streptozotocin-induced) rats were fed high fat semipurified diets providing a high or low polyunsaturated to saturated fatty acid (P/S) ratio. Feeding a high P/S diet increased the polyunsaturated fatty acid content of major membrane phospholipids of the adipocyte plasma membrane from both normal and diabetic animals. The diabetic state was associated with an elevated content of linoleic acid and a reduced level of arachidonic acid consistent with reduced delta 6-desaturation. Feeding the high P/S diet to diabetic animals increased membrane linoleic acid content and prevented the decrease observed in the arachidonic acid of membrane phospholipids. The high P/S diet was associated with increased insulin binding in nondiabetic animals but did not change the amount of insulin bound by cells from diabetic animals. Significantly (p less than 0.05) increased rates of insulin-stimulated glucose transport and lipogenesis (glucose incorporation into lipids) were observed in control animals fed the high as compared to the low P/S diet. The rates of insulin-stimulated glucose transport, oxidation, and lipogenesis were lower (p less than 0.05) for cells from diabetic as compared to control animals. However, feeding a high P/S diet significantly improved rates for all three of these functions (p less than 0.05). It is concluded that diet-induced alterations in membrane composition may provide a mechanism for improving the cellular response to insulin in cells from diabetic animals.

Chronic and endogenous regulation of insulin receptors by catecholamines in adipocytes from patients with a phaeochromocytoma

Insulin binding in adipocytes from patients with a phaeochromocytoma (PH) approached that of the controls (C) at low and higher concentrations of unlabeled insulin. The apparent receptor affinity was unchanged (ED50: PH 0.50 x 10(-9) M and C 0.60 x 10(-9) M). Scatchard analysis of the binding data using the negative cooperative model revealed a 46% decrease in the total number of receptors together with no changes in both K-e (PH 0.55 x 10(9) M-1 and C 0.36 x 10(9) M-1) and K-f (PH 0.13 x 10(9) M-1 and C 0.07 x 10(9) M-1). According to the two site model, an altered proportion in the two classes of insulin binding sites was detected. This was accompanied by a catecholamine-desensitization of the adipocytes to the antilipolytic action of insulin. These events could represent a final situation of a chronic and endogenous regulation by high levels of catecholamines of insulin receptors in human adipose tissue.

The Role of Insulin Receptor Sulphydryl Groups in Insulin Binding and Cellular Response in Rat Adipocytes

Phenylarsine oxide (PAO), an agent which reacts with vicinal sulphydryl groups and dithiothreitol (DTT), a disulphide reducing agent, inhibited insulin binding to intact adipocytes with half maximal inhibition occurring at 28 microM and 340 microM, respectively. Pretreatment of adipocytes with DTT (2mM) prevented insulin stimulation of glucose uptake by approximately 50%. The marked inhibition of insulin binding to adipocytes by PAO and DTT is consistent with the involvement of the receptor cysteine-rich region of hormone binding. Furthermore, DTT inhibition of insulin binding suggests that the integrity of disulphide bridges is critical for insulin binding. The inhibitory effect of DTT and PAO on insulin binding were not additive, instead addition of DTT to PAO-treated adipocytes effected 15% reversal of binding inhibition. The marked inhibition of insulin binding by addition of low concentrations of DTT (0.2-2.0mM) to intact adipocytes is in contrast to the previously reported biphasic response for the effect of DTT on insulin binding to isolated plasma membranes from rat adipocytes (Schweitzer et al. Proc. Natl. Acad. Sci. U.S.A. 77, 4692-4696, 1980). Scatchard plots for 125I-iodoinsulin binding to adipocytes in the basal state were linear. In contrast, Scatchard analysis of insulin binding to plasma membranes prepared from both basal and insulin-stimulated adipocytes yielded severely curvilinear plots. The data suggests that (i) fundamental differences exist between the receptor state in intact cells and isolated plasma membranes and (ii) that a disulphide-rich region within the insulin receptor, other than the previously reported class I and class II disulphide bridges, is critical for insulin binding and cellular response.

Development of insulin sensitivity in white adipose tissue during the suckling-weaning transition in the rat. Involvement of glucose transport and lipogenesis.

The changes of insulin responsiveness of white adipose tissue during the suckling-weaning transition in the rat were investigated in vitro on isolated adipocytes. Insulin binding, glucose transport and glucose metabolism in adipocytes from suckling rats and from rats weaned on to a high-carbohydrate (HC) or a high-fat (HF) diet were compared. Despite similar insulin binding, insulin-stimulated glucose transport rate is lower in adipocytes from suckling rats and HF-weaned rats than in adipocytes from HC-weaned rats. Moreover, whereas insulin markedly stimulates glucose metabolism in adipocytes from HC-weaned rats, glucose metabolism is totally unresponsive to insulin in adipocytes from suckling and HF-weaned rats. This insulin resistance is associated with a very low rate of lipogenesis and low activities of acetyl-CoA carboxylase, fatty acid synthase and pyruvate dehydrogenase.

Effect of long-term nickel ingestion on insulin binding and antilipolytic response in rat adipocytes

Male Wistar rats of the third generation of rats drinking 200 micrograms Ni2+/mL as NiCl2 in their drinking water were studied. Basal plasma glucose and insulin levels were unchanged. Epididymal adipocytes from Ni2(+)-fed rats showed an increased insulin binding with a slight increase in apparent insulin affinity (ED50: Ni2(+)-fed rats 2.8 x 10(-9) M and controls 5 x 10(-9) M) with no change in insulin receptor numbers (Ni2(+)-fed rats 143,000 +/- 12,000 (6) receptors/cell and controls 126,000 +/- 13,000 (5]. Moreover, a decreased sensitivity to the antilipolytic response of insulin was also observed in adipocytes from Ni2(+)-fed rats. These events could represent actions of Ni2+ both at the receptor and post-receptor insulin levels. Several possible mechanisms involved in the process are suggested.

The Effects of Metformin on Adipocyte Insulin Action and Metabolic Control in Obese Subjects with Type 2 Diabetes

To investigate the mechanisms of action of metformin, insulin receptor binding and the activity of several insulin-controlled metabolic pathways were measured in adipocytes taken from 10 obese Type 2 diabetic patients treated for 4 weeks with either metformin (0.5 g x 3 daily) or matching placebo using a double-blind crossover design. Metformin therapy was associated with a significant fall in serum fructosamine levels (3.1 +/- 0.4 vs 2.8 +/- 0.4 mmol l-1, p less than 0.02) as well as fasting (10.8 +/- 2.4 vs 9.4 +/- 2.1 mmol l-1) and daytime (11.5 +/- 2.4 vs 10.0 +/- 2.2 mmol l-1) plasma glucose concentrations (p less than 0.05). Fasting and postprandial plasma levels of C-peptide and insulin were unchanged. While fasting plasma lactate concentrations remained unaltered after metformin, a rise was noted in response to meals (from 1.4 +/- 0.1 to 1.8 +/- 0.2 mmol l-1, p less than 0.05). Adipocyte insulin receptor binding was unaffected by drug treatment. Moreover, no insulin-like effects or post-binding potentiation of insulin action could be found on adipocyte glucose transport, glucose oxidation, lipogenesis, glycolysis or antilipolysis. A complementary in vitro study using adipocytes from non-obese healthy volunteers failed to show any direct effect of metformin on adipocyte insulin binding or glucose transport and metabolism, at media drug concentrations corresponding to therapeutic plasma levels.

Insulin binding and action on adipocytes from female rats with experimentally induced chronic hyperprolactinemia

We studied insulin binding and action in adipocytes from female rats with chronic hyperprolactinemia induced by grafting an anterior pituitary gland under the right kidney capsule. Normal basal insulin plasma levels were detected. An increase in insulin binding due to an increased number of receptors was observed (grafted: 193000 ±13000 (6) receptors/cell vs. controls: 136000 ± 17000 (6) receptors/cell, P < 0.05). No changes in receptor affinity were detected (ED 50 grafted: 2.3 × 10 −9 M and ED 50 controls: 1.6 × 10 −9 M). The antilipolytic activity of insulin was significantly decreased in adipocytes from rats with hyperprolactinemia, indicating an insulin-resistant state in these animals. These findings suggest that the chronic hyperprolactinemic state can modify receptor and post-receptor insulin events in rat parametrial adipose tissue.

Relationships between cell surface insulin binding and endocytosis in adipocytes.

Chymotrypsin substrate analogues, such as N-acetyl-Tyr ethyl ester, have recently been demonstrated to inhibit the endocytic uptake of insulin in isolated rat adipocytes. In this study, the effects of N-acetyl-Tyr ethyl ester on cell surface insulin binding and dissociation were examined. Surface-bound 125I-insulin was distinguished from intracellular 125I-insulin by the sensitivity of the former to rapid dissociation with an acidic buffer (pH 3.0). Plateau levels of surface-bound insulin at 37 degrees C were increased 70% by inhibiting the internalization pathway. This increase was temperature and insulin concentration dependent. Thus differences in surface binding were small at 12 degrees C and also at high (100-200 ng/ml) insulin concentrations. Inhibition of internalization with N-acetyl-Tyr ethyl ester markedly slowed the loss of surface-bound insulin observed during dissociation studies. After 20-30 min of dissociation, the remaining levels of surface-bound insulin were three- to fourfold higher in treated adipocytes compared with control adipocytes. Added unlabeled insulin retained its ability to accelerate the dissociation of insulin in N-acetyl-Tyr ethyl ester-treated cells. These observations indicate that the internalization pathway is a quantitatively important factor in determining levels of surface binding at 37 degrees C and in determining the rate of deactivation of insulin binding.

Effect of exercise on insulin binding and glucose transport in adipocytes of normal humans.

Acute exercise increases insulin binding to its receptors on blood cells. Whether the enhanced insulin binding explains the exercise-induced increase in glucose uptake is unclear, since insulin binding and glucose uptake have not been measured simultaneously in a target tissue of insulin. In this study, we determined insulin binding and the rate of glucose transport in adipocytes obtained by needle biopsy from 10 healthy men before and after 3 h of cycle-ergometric exercise. During the exercise, plasma glucose (P less than 0.01) and insulin (P less than 0.001) fell and serum free fatty acid level rose 4.3-fold (P less than 0.001). 125I-insulin binding to adipocytes remained unchanged during exercise. The rate of basal glucose transport clearance fell from 28.1 +/- 5.7 fl.cell-1.s-1 to 22.9 +/- 5.6 fl.cell-1.s-1 (P less than 0.005), and the insulin-stimulated increase in glucose transport rate rose from 196 +/- 26 to 279 +/- 33% (P less than 0.025) during the exercise. Thus, in the adipocytes during exercise, the basal glucose transport rate and the responsiveness of glucose transport to insulin changed in the absence of alterations in insulin binding. These data indicate that the exercise-induced changes in insulin binding show tissue specificity and do not always parallel alterations in glucose transport.

Decreased insulin binding and antilipolytic response in adipocytes from patients with Cushing's syndrome.

Human adipocytes from patients with chronic endogenous hypercortisolism (Cushing's syndrome) showed a statistically significant decrease in insulin binding at low unlabelled-insulin concentrations but no change in receptor numbers (Cushing's 180,000 +/- 48,000 (3) receptors/cell and controls 189,000 +/- 30,000 (7)) together with a fourfold decrease in apparent receptor affinity (ED50: Cushing's 2.25 x 10(-9) M and controls 0.57 x 10(-9) M) and a decreased sensitivity to the antilipolytic effect of insulin. These events could represent the final situation of a chronic and endogenous regulation by high levels of cortisol of insulin receptors in human adipose tissue.

Dissociation of in vitro sensitivities of glucose transport and antilipolysis to insulin in NIDDM.

It is unclear from previous studies whether qualitative or only quantitative differences exist in insulin action in adipocytes obtained from obese subjects with non-insulin-dependent diabetes mellitus (NIDDM) when compared with equally obese nondiabetic subjects. In addition, the role of changes in insulin binding as a cause of insulin resistance in NIDDM is still controversial. We compared the sensitivities of glucose transport and antilipolysis to insulin and measured insulin binding in abdominal adipocytes obtained from 45 obese nondiabetic (% fat, 41 +/- 1), 25 obese diabetic (% fat, 40 +/- 1), and 15 nonobese (% fat, 30 +/- 1) female southwestern American Indians. Compared with the nonobese group, the sensitivities of glucose transport and antilipolysis were reduced in both the obese nondiabetic and obese diabetic groups. Compared with the obese nondiabetic subjects, the ED50 for stimulation of glucose transport was higher in the obese patients with NIDDM (171 +/- 38 vs. 92 +/- 10 pM, P less than 0.005). In contrast, the ED50s for antilipolysis were similar in obese diabetic patients (32 +/- 6 pM) and obese nondiabetic subjects (27 +/- 3 pM). No difference was found in insulin binding in patients with NIDDM when compared with the equally obese nondiabetic subjects. These data indicate 1) the mechanism of insulin resistance differs in NIDDM and obesity, and 2) the selective loss of insulin sensitivity in NIDDM precludes changes in insulin binding as a cause of insulin resistance in this disorder.

Adipocyte insulin binding and action in moderately obese NIDDM patients after dietary control of plasma glucose: reversal of postbinding abnormalities.

Studies of fat cells from patients with newly diagnosed, untreated non-insulin-dependent diabetes mellitus (NIDDM) have revealed severe abnormalities in insulin action on glucose transport and metabolism. To determine whether these defects can be reversed if good glycemic control is reached by dietary treatment, eight moderately obese NIDDM subjects were studied at diagnosis and again when the patients had been in good glycemic control induced by low-energy dieting for at least 2 mo (absence of glycosuria and fasting plasma glucose less than 7 mM). Average body weight decreased by 8 kg (P less than .05). Fasting plasma glucose decreased from 11.5 +/- 1.2 to 6.9 +/- 0.9 mM, whereas fasting serum insulin concentrations were unchanged. Adipocyte insulin binding at tracer concentration (15 pM, 37 degrees C) was not changed significantly (1.94 +/- 0.52 to 2.05 +/- 0.62% per 30 cm2 surface area/ml). The basal (non-insulin-stimulated) glucose transport (tracer glucose concentration 5 microM) increased from 25 +/- 12 to 44 +/- 14 pmol X 90 min-1 X 10 cm-2 surface area (P less than .02). The maximally insulin-stimulated glucose transport rate increased from 35 +/- 20 to 78 +/- 26 pmol/90 min (P less than .01). The percentage insulin response above basal levels increased from 31 +/- 40 to 89 +/- 58% (P less than .01). The insulin sensitivity (half-maximally stimulating insulin concentrations) was also improved (P less than .05). Glucose conversion rates to total lipids increased 34 +/- 62 and 65 +/- 80% in basal cells and maximally insulin-stimulated cells, respectively (.2 greater than P greater than .1, .1 greater than P greater than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-receptor kinase activity of adipose tissue from morbidly obese humans with and without NIDDM.

We have determined glucose transport, insulin binding, and insulin-receptor kinase activity in adipose tissue from morbidly obese patients with and without non-insulin-dependent diabetes mellitus (NIDDM). The insulin sensitivity and responsiveness of glucose transport in freshly isolated adipocytes were significantly reduced in NIDDM subjects compared with nondiabetics. This was due in part to decreased insulin binding in adipocytes. Reduced specific 125I-labeled insulin binding was also observed in crude detergent extracts and partially purified insulin receptors from adipose tissue. In addition, the basal and insulin-stimulated tyrosine-specific protein kinase activity per milligram of protein was significantly decreased in NIDDM patients compared with nondiabetics. The differences between maximally insulin-stimulated and basal kinase activities expressed by insulin-binding activity were also significantly reduced in NIDDM subjects. We conclude that insulin resistance in morbidly obese patients with NIDDM is due to both insulin-binding and postbinding defects. One of the postbinding defects in NIDDM appears to be impaired insulin-receptor kinase activity of fat tissue.