Hyperfunction of the entero-PP axis in non-insulin dependent diabetes mellitus

In a previous study we have found that the plasma pancreatic polypeptide (PP) response to oral glucose loading is exaggerated in diabetic patients compared with normal subjects. We have investigated, therefore, the effects of a protein-rich meal or meat extract ingestion on plasma PP secretion and examined also the effects of intravenous arginine administration on PP levels in normal subjects and in patients with noninsulin-dependent diabetes mellitus (NIDDM). Following a 600 Kcal meal ingestion, plasma PP levels increased immediately and showed biphasic secretion in normal subjects and in NIDDM, but the response was exaggerated in NIDDM. A 50 g meat extract administration also produced an exaggerated PP response in NIDDM compared with normal subjects. In NIDDM and normal subjects, plasma PP levels did not change significantly during an arginine infusion (30 g for 45 min) but after the end of the infusion PP levels increased significantly compared with basal levels. In normal subjects, plasma PP rose abruptly after a bolus arginine injection (4 g for 2 min) and then remained at significantly high levels even 30 min after the injection. In NIDDM, however, plasma PP levels tended to increase, but not significantly, after the bolus arginine injection. Since in NIDDM the protein-rich meal and meat extract ingestion produced an exaggerated rise in plasma PP while the PP responses to the intravenous arginine administration were rather impaired compared with normal subjects, we suggest that the entero-PP axis is overactive in NIDDM.     

Postprandial glucose, insulin and glucagon responses to meals with different nutrient compositions in non-insulin-dependent diabetes mellitus

Postprandial glycaemic and hormone responses to meals with different nutrient compositions and their heterogeneity were evaluated in 16 non-insulin-dependent diabetic patients and 5 healthy volunteers. Five kinds of nutrient stimulation--75 g glucose, a Japanese mixed meal (400 kcal, carbohydrate 60%, protein 14%, fat 26%), a high protein meal (300 kcal, C 26%, P 64%, F 10%), a high fat meal (300 kcal, C 23%, P 5%, F 72%) and 20 g iv glucose--was given to each subject. On the average, in both normal and diabetic subjects, the increases in plasma glucose (PG) and insulin (IRI) were the largest with the oral glucose load and the smallest with the high protein meal. The ratio of increase in IRI and PG (sigma delta IRI/sigma delta PG) was the highest with the high protein meal and the lowest with the oral glucose load. sigma delta IRI with the high protein meal and the high fat meal were the same in normal and diabetic subjects. However, each of the 16 NIDDM patients and 5 normal volunteers exhibited a different pattern of response to the nutrient stimuli and no definite subgroup could be classified. There was no correlation between metabolic responses and family history of diabetes mellitus, duration of diabetes, body mass index and fasting plasma glucose. The present results suggest the nearly intact capacity of insulin secretion in NIDDM in response to a high protein or high fat meal and the difficulty of subclassification in NIDDM according to the glycaemic and hormone responses to the different nutrient stimuli.     

Characterization of the insulin resistance in liver cirrhosis: a comparison with non-insulin dependent diabetes mellitus.

To characterize the mechanisms of insulin resistance in liver cirrhosis (LC), we estimated the peripheral tissue sensitivity and responsiveness to insulin using the euglycemic clamp technique and determined the insulin binding to erythrocytes in patients with compensated LC as well as in patients with non-insulin dependent diabetes mellitus (NIDDM). The insulin dose-response curves of the glucose metabolic clearance rates (MCR) were shifted to the right and downward both in patients with LC and NIDDM, indicating a reduced sensitivity and responsiveness to insulin. In the cirrhotics, MCR at the maximally effective insulin level, an index of insulin responsiveness, was correlated with fasting insulin levels (r = -0.57, P < 0.01) and sigma BG in 75 gOGTT (r = -0.43, P < 0.05), but no correlations were found between them and the diabetics. Although specific insulin bindings to erythrocytes were significantly lower in patients both with LC and NIDDM, Scatchard analysis revealed a significant decrease in the number of insulin receptors in the cirrhotics, and a decrease in the empty-site affinity in the diabetics. These findings suggest that insulin resistance in LC consists of a combination of binding and postbinding defects. The latter defect may be caused by basal hyperinsulinemia and contribute to the development of glucose intolerance. Although binding and postbinding abnormalities are also found in NIDDM, the mechanisms of insulin resistance in LC and NIDDM may be different.     

Is the insulin resistance of patients with noninsulin-dependent diabetes mellitus secondary to insulin deficiency?

Defects in both insulin secretion and action have been documented in patients with noninsulin-dependent diabetes mellitus (NIDDM), leading to the suggestion that both fasting hyperglycemia and insulin resistance in NIDDM are secondary to insulin deficiency. In order to test this hypothesis, insulin secretion (plasma insulin response to oral glucose) and insulin action (insulin clamp) were determined in 25 patients with NIDDM. The results documented relationships between incremental plasma insulin response to glucose and degree of fasting hyperglycemia (r = -.045, P less than 0.05) and insulin-stimulated glucose utilization (r = 0.25, P = NS). These data indicate that differences in insulin secretory response accounted for only approximately 20% of the variance in fasting plasma glucose level and 6% of the variance in insulin resistance in NIDDM. Thus, differences in insulin-secretory response contribute modestly to magnitude of glycemia, and not at all to variations in insulin resistance in NIDDM, permitting rejection of the hypothesis that insulin resistance is secondary to insulin deficiency.     

Erythrocyte insulin binding abnormalities in fibro calculous pancreatic diabetes

Insulin binding to erythrocyte insulin receptors was studied in 17 patients (13 men and 4 women) with fibrocalculous pancreatic diabetes mellitus (FCPD) and compared with that of 14 newly diagnosed NIDDM patients matched for age, sex and severity of hyperglycemia, and 14 age and sex-matched non-diabetic control subjects. In the uncompensated diabetic state, mean (+/- S.D.) specific binding of insulin was lower in both FCPD and NIDDM patients, compared with non-diabetic controls (P less than 0.001). Control of diabetes with short term therapy (2-6 weeks) resulted in a significant improvement in the mean specific insulin binding in both FCPD and NIDDM patients (P less than 0.001) due to increased binding affinity in the former, and increased affinity and the number of binding sites in the latter. As compared to short term therapy, chronic therapy (5-8 months) in FCPD patients resulted in a marginal decrease in specific insulin binding. However, this was still significantly higher than the basal value (P less than 0.05). FCPD patients had an initial low mean basal plasma IRI and a much lower mean stimulated IRI response as compared to NIDDM and non-diabetic controls.     

Reference intervals for glucose, beta-cell polypeptides, and counterregulatory factors during prolonged fasting

To establish reference intervals for the pancreatic beta-cell response and the counterregulatory hormone response to prolonged fasting, we studied 33 healthy subjects (16 males, 17 females) during a 72-h fast. Glucose, insulin, C-peptide, and proinsulin levels decreased (P < 0.001), and the levels of counterregulatory factors increased during the fast [P < 0.05; glucagon and free fatty acids (FFA) with a linear increase and epinephrine, norepinephrine, and cortisol with a clear underlying circadian rhythm]. Growth hormone secretion increased from the first to third day of fasting (P < 0.05) but actually decreased from the second to third day of fasting (P = 0.03). Males had higher glucose and glucagon levels and lower FFA levels during the fast (P < 0.05), whereas no effect of gender on beta-cell polypeptides was observed. A high body mass index resulted in higher insulin and C-peptide levels during the fast (P < 0.05). In conclusion, we have provided reference intervals for glucoregulatory factors during a 72-h fast. We observed a diminished beta-cell response concomitant with an increased secretion of counterregulatory hormones. These results should be of clinical and scientific value in the investigation of hypoglycemic disorders.     

Role of obesity and hyperinsulinemia in the insulin resistance of obese subjects with the clinical triad of polycystic ovaries, hirsutism and acanthosis nigricans

The insulin resistance of 4 nonobese and 8 obese patients with polycystic ovaries, hirsutism and benign acanthosis nigricans, and of 6 'obese normal' apart from obesity and 10 normal female subjects was evaluated by means of an intravenous insulin tolerance test and by measuring basal and insulin responses to an oral glucose load. The patients with polycystic ovaries, hirsutism and acanthosis had a decreased hypoglycemic response to exogenous insulin. The subjects with polycystic ovaries presented a significantly greater mean glucose response area for the same or greater mean insulin response area than the obese or nonobese normal subjects. The insulin resistance in the patient with polycystic ovaries, hirsutism and acanthosis nigricans could not be exclusively ascribed to a reduced receptor number, but also appeared to be due to a simultaneous postbinding defect probably related to the high insulin levels in patients with polycystic ovaries be they obese or not. The elevated plasma androgens and the presence of acanthosis found in these patients are likely also related to the hyperinsulinemia. To evaluate the influence of obesity, obese and nonobese patients with acanthosis nigricans and polycystic ovaries were compared. Higher insulin levels were found in the thin subjects, which could explain their greater insulin resistance and more severe hyperandrogenism. The comparison between obese patients with and those without acanthosis nigricans and polycystic ovaries suggested that, despite similar insulin levels, the greater known duration of obesity (probably also of the hyperinsulinemia) of the former was a possible explanation for their more intense insulin resistance and higher testosterone levels.     

Mechanism of methaemoglobin reduction by human erythrocytes.

The effect of alterations to the insulin receptor on the insulin sensitivity of isolated adipocytes was studied. Receptor changes were induced by treatment of adipocytes with either phospholipase C or trypsin. After enzyme treatment, binding of insulin to insulin receptors and insulin-mediated glucose metabolism were examined. Exposure of adipocytes to phospholipase C (2 units/ml) significantly increased insulin binding to the cells, but destroyed the ability of the cells to oxidize glucose. After treatment with trypsin (500 micrograms/ml) for 5 min, insulin binding to the adipocytes was significantly increased. This was shown to be due to an increase in insulin-receptor affinity. Metabolic studies showed that trypsin treatment led to an increase in basal glucose transport but markedly decreased the response to insulin at all concentrations tested. Adipocytes treated with trypsin showed no significant difference in basal glucose oxidation rates when compared with controls, but were less sensitive to insulin at low insulin concentrations, and showed a decreased maximum response at high insulin concentrations. In conclusion, these findings indicate a dissociation between induced changes in binding of insulin to insulin receptors and subsequent hormone action. The importance of post-receptor events in the biological action of insulin is highlighted.     

Insulin action in skeletal muscle from patients with NIDDM

Insulin resistance in peripheral tissues is a common feature of non insulin-dependent diabetes mellitus (NIDDM). The decrease in insulin-mediated peripheral glucose uptake in NIDDM patients can be localized to defects in insulin action on glucose transport in skeletal muscle. Following short term in vitro exposure to both submaximal and maximal concentrations of insulin, 3-O-methylglucose transport rates are 40-50% lower in isolated skeletal muscle strips from NIDDM patients when compared to muscle strips from nondiabetic subjects. In addition, we have shown that physiological levels of insulin induce a 1.6-2.0 fold increase in GLUT4 content in skeletal muscle plasma membranes from control subjects, whereas no significant increase was noted in NIDDM skeletal muscle. Impaired insulin-stimulated GLUT4 translocation and glucose transport in NIDDM skeletal muscle is associated with reduced insulin-stimulated IRS-1 tyrosine phosphorylation and PI3-kinase activity. The reduced IRS-1 phosphorylation cannot be attributed to decreased protein expression, since the IRS-1 protein content is similar between NIDDM subjects and controls. Altered glycemia may contribute to decreased insulin-mediated glucose transport in skeletal muscle from NIDDM patients. We have shown that insulin-stimulated glucose transport is normalized in vitro in the presence of euglycemia, but not in the presence of hyperglycemia. Thus, the circulating level of glucose may independently regulate insulin stimulated glucose transport in skeletal muscle from NIDDM patients via a down regulation of the insulin signaling cascade.     

Insulin-stimulated glucose uptake and fasting blood glucose.

Changes in insulin-stimulated glucose metabolism were studied in young and aged subjects, subjects with impaired glucose tolerance, and patients with NIDDM by means of the glucose clamp technique. The diabetic group includes obese and non-obese patients treated without insulin and non-obese patients treated with insulin. The glucose disposal rate (GDR) was decreased in aged subjects (5.8 +/- 0.4 mg/kg/min) compared with young controls (7.4 +/- 0.3 mg/kg/min). In patients with IGT, it was further decreased to 3.6 +/- 0.5 mg/kg/min, which was comparable to the rate in NIDDM without insulin treatment (3.3 +/- 0.4 mg/kg/min). There were no differences in the GDR between obese (3.0 +/- 0.3 mg/kg/min) and non-obese (3.4 +/- 0.6 mg/kg/min) diabetic patients. In insulin-treated diabetic patients, GDR ranged widely, but the mean value was partially normalized (5.2 +/- 0.9 mg/kg/min). In the diabetic group, no correlation was observed between fasting blood glucose and GDR. These results suggest that in the course of developing NIDDM, a decrease in insulin-stimulated glucose uptake precedes a rise in fasting blood glucose. Thus, as previously reported for Caucasian NIDDM patients, resistance to insulin-stimulated glucose uptake may be one of the basic defects in Japanese patients with NIDDM. The degree of glycemia, however, is not directly related to the magnitude of the defect in insulin action.     

Cyclic AMP modulates insulin binding and induces post-receptor insulin resistance of glucose transport in isolated rat adipocytes

The effect of cAMP on insulin binding and insulin stimulation of glucose transport was investigated in isolated rat adipocytes. Preincubation for 30 min in medium containing 16 mmol/l glucose and either db-cAMP or bromo-cAMP in concentrations of 10(-4)-10(-3) M inhibited high affinity binding of insulin by 15 to 30% and glucose transport by 30 to 50%. Preincubation with IBMX (10(-4)-10(-3) M) reduced insulin binding by 25% and glucose transport by 70%. Closer analysis of these data indicated that preincubation with these compounds caused not only a decrease in insulin binding but also a post-receptor resistance. High intracellular cyclic AMP-levels seem therefore to induce insulin resistance at both receptor and post-receptor levels.     

Autonomic Control of Insulin Secretion and the Treatment of Heart Failure

To investigate the role of the autonomic nervous system in controlling insulin secretion 13 normal subjects and 5 patients with heart failure underwent insulin secretion tests. Alpha-adrenergic stimulation and beta-receptor blockade significantly depressed the secretion of insulin in response to intravenous tolbutamide in normal subjects, while both alpha-blockade and beta-stimulation significantly increased the insulin secretion response in both normal subjects and patients in heart failure. Parasympathetic stimulation and blockade had no significant effect on the insulin secretion response. These findings suggest that drugs that block the alpha-adrenergic receptors or stimulate the beta-adrenergic receptors by their ability to counteract the insulin suppression resulting from increased sympathetic nervous activity may play a vital metabolic part in the deranged metabolism of the failing heart in addition to their direct haemodynamic benefits.     

Effect of pharmacological doses of oxytocin on insulin response to glucose in normal man

In this study we have examined the effect of the administration of oxytocin on basal blood concentrations of insulin, glucagon, cortisol, growth hormone, and on the dynamic secretory response of these hormones to intravenous glucose administration (0.33 g/kg) in basal condition and after the injection of 3 IU (1 plus 2 IU/1 h) or 6 IU (2 plus 4 IU/1 h) of oxytocin (6 subjects for each group). The highest dose of oxytocin (6 IU) used significantly increased insulin secretion in response to intravenously administered glucose. No significant change of insulin secretion was observed with 3 IU of oxytocin. Glucagon, cortisol, and growth hormone response to intravenous injection of glucose was not affected by oxytocin (3 or 6 IU) administration. These results suggest that high doses of oxytocin affect beta-cell function in normal man.     

Insulin resistance in Fibrocalculous (tropical) pancreatic diabetes

Insulin resistance was assessed by Insulin Tolerance Test (ITT) in 12 patients with FCPD, 10 with NIDDM and 12 age and sex matched control subjects. The mean BMI of the FCPD was lower than the NIDDM and control groups (P less than 0.001). There was no significant difference between the mean fasting plasma glucose or HbA1 between the FCPD and NIDDM patients. The mean fasting C-peptide of the FCPD group was significantly lower than the NIDDM and control groups (P less than 0.001). The mean glucose disposal rate (KITT) was 5.57 +/- 2.28 in the control group, 2.15 +/- 2.00 in the FCPD and 1.77 +/- 0.91 in the NiDDM group (P less than 0.001, control vs FCPD and NIDDM). The difference in KITT between FCPD and NIDDM groups was not significant statistically. The data suggests that patients with FCPD have evidence of insulin resistance and this is similar to that seen in NIDDM patients.     

Mechanism, temporal patterns, and magnitudes of the metabolic responses to the KATP channel agonist diazoxide

To assess the mechanism, temporal patterns, and magnitudes of the metabolic responses to the ATP-dependent potassium channel agonist diazoxide, neuroendocrine and metabolic responses to intravenous diazoxide (saline, 1.0 and 2.0 mg/kg) and oral diazoxide (placebo, 4.0 and 6.0 mg/kg) were assessed in healthy young adults. Intravenous diazoxide produced rapid, but transient, decrements (P = 0.0023) in plasma insulin (e.g., nadirs of 2.8 +/- 0.5 and 1.8 +/- 0.3 microU/ml compared with 7.0 +/- 1.0 microU/ml after saline at 4.0-7.5 min) and C-peptide (P = 0.0228) associated with dose-related increments in plasma glucose (P = 0.0044) and serum nonesterified fatty acids (P < 0.0001). After oral diazoxide, plasma insulin appeared to decline, as did C-peptide, again associated with dose-related increments in plasma glucose (P < 0.0001) and serum nonesterified fatty acids (P = 0.0141). Plasma glucagon, as well as cortisol and growth hormone, was not altered. Plasma epinephrine increased (P = 0.0215) slightly only after intravenous diazoxide. There were dose-related increments in plasma norepinephrine (P = 0.0038 and P = 0.0005, respectively), undoubtedly reflecting a compensatory sympathetic neural response to vasodilation produced by diazoxide, but these would not raise plasma glucose or serum nonesterified fatty acid levels. Thus selective suppression of insulin secretion, without stimulation of glucagon secretion, raised plasma glucose and serum nonesterified fatty acid concentrations. These findings define the temporal patterns and magnitudes of the metabolic responses to diazoxide and underscore the primacy of regulated insulin secretion in the physiological regulation of postabsorptive carbohydrate and lipid metabolism.     

Effect of short- and long-term chlorpropamide therapy on oral glucose tolerance and erythrocyte insulin receptors in non-obese non-insulin dependent diabetes mellitus

Erythrocyte (RBC) insulin receptors and the insulin response to glucose load (oGTT) were evaluated in ten male, non-obese, non-insulin dependent diabetic patients (NIDDM) before and after 14 and 90 days of 250 mg/day of chlorpropamide administration. In addition, as a control group, twelve healthy non-obese subjects were studied. Diabetic patients with fasting plasma glucose level higher than 14 mmol/l (group A), presented a significant improvement in the incremental glucose area only after 90 days of therapy. There was an evident reduction in insulin secretion, in comparison to normals, which however increased progressively during drug administration. No alterations in insulin binding to RBC receptors were observed either before or after the use of chlorpropamide, but the normalization of the initially low number of receptors per cell (N) and an increased high affinity constant (Ke) were achieved. In group B with fasting glucose less than 14 mmol/l there was a significant reduction in plasma glucose levels during oGTT without changes in glucose areas and a significant improvement of the insulin secretion was noted only in the early samples. Except for transient alterations in N and Ke no significant changes were observed in insulin-RBC binding parameters. We conclude that the improvement in the glucose tolerance in NIDDM is associated both to a greater insulin secretion and to the correction of the alterations in receptor parameters which could be related, at least partially, to proportionate changes in reticulocyte count.     

Postprandial changes in cytosolic free calcium and glucose uptake in adipocytes in obesity and non-insulin-dependent diabetes mellitus

We evaluated the possible relationship between [Ca2+]i and glucose uptake in the postabsorptive state and postprandially in adipocytes obtained from normal and obese subjects, as well as from patients with non-insulin-dependent diabetes mellitus (NIDDM). Adipocytes isolated from overnight-fasted obese and NIDDM patients revealed high levels of [Ca2+]i (p less than 0.05 vs. control) in association with a decreased insulin-stimulated glucose uptake (p less than 0.05 vs. controls). In obese and NIDDM patients treated with oral hypoglycemic agents, the overnight fasting levels of [Ca2+]i were increased postprandially (p less than 0.05), concomitantly with a further decrease in insulin-stimulated 2-deoxyglucose uptake. Although the precise nature of the relationship between [Ca2+]i in specific insulin target tissues and diminished insulin action remains unknown, it is clear that high levels of [Ca2+]i may contribute to the development of insulin resistance.     

Hypoglycaemia and counterregulation during childhood

Hypoglycaemia is particularly common in young children with type 1 diabetes mellitus yet the normal protective counterregulatory responses have been little studied in this age group. The studies reported have shown conflicting results, in part related to prior glycaemic control and also to the method of investigation used. Counterregulatory hormone responses during both spontaneous and experimentally induced episodes of nocturnal hypoglycaemia do appear to be blunted, which may be a function of sleep itself. Although studies of cognitive function have consistently shown defects in certain areas of neurocognitive performance, particularly in those children with early-onset diabetes or a prior history of severe hypoglycaemia, the contribution of nocturnal hypoglycaemia to the development of these impairments has not been evaluated. In young adults and adolescents, nocturnal hypoglycaemia has been linked to cardiac arrhythmia and the risk of sudden death. The development of new techniques for continuous subcutaneous glucose monitoring may allow detailed study of counterregulatory responses and symptom recognition in young children. Effective intensification of insulin therapy without an increased risk of hypoglycaemia may be possible using new insulin analogues or continued subcutaneous intravenous infusion (CSII), thus improving patient compliance and overall quality of clinical care.     

Relation of cholesterol metabolism and non-cholesterol sterols to insulin resistance

Using non-cholesterol sterols investigation several authors postulated a hypothesis that in the metabolic syndrome cholesterol endogenous synthesis is increased and its absorption decreased. Our study is the first attempt to evaluate the direct relation of cholesterol metabolism to the principal pathogenetic phenomenon of the metabolic syndrome--namely to insulin resistance. We have measured insulin sensitivity by two methods--Quicki (Quantitative Sensitivity Check Index) and intravenous insulin tolerance test (Kitt) and 3 indirect markers--fasting insulin level, fasting C-peptide level and SHBG (sex hormone binding globulin). The investigation was performed in three groups of subjects with a different prevalence of insulin resistance: 72 non-diabetics with ischemic heart disease, 117 young blood donors and 63 type 2 diabetics on diet therapy only. Analyzing altogether 60 relationships--between four sterols (lathosterol, squalene, sitosterol and campesterol) and five markers of insulin resistance in three groups of subjects--we have found only six significant relations between cholesterol synthesis and absorption and insulin resistance in all groups of patients. Our results indicate that there exists a significant relationship between insulin sensitivity and indices of either increased cholesterol synthesis or decreased cholesterol absorption. Insulin resistance explains only a part of both abnormalities mentioned above.     

Association of the insulin-receptor variant Met-985 with hyperglycemia and non-insulin-dependent diabetes mellitus in the Netherlands: a population-based study.

One of the characteristics of non-insulin-dependent diabetes mellitus (NIDDM) is the presence of insulin resistance. Most NIDDM patients have a normal sequence of the insulin receptor, indicating that, if insulin-receptor mutations contribute to the development of NIDDM, they will be present only in a minor fraction of the NIDDM population. The goal of the present study was to examine whether insulin-receptor mutations contribute to the development of NIDDM. We examined 161 individuals with NIDDM and 538 healthy controls from the population-based Rotterdam study for the presence of mutations in the insulin-receptor gene by SSCP. A heterozygous mutation changing valine-985 into methionine was detected in 5.6% of diabetic subjects and in 1.3% of individuals with normal oral glucose tolerance test. Adjusted for age, gender, and body-mass index, this revealed a relative risk for diabetes of 4.49 (95% confidence interval 1.59-12.25) for Met-985 carriers. When the total study group was analyzed, the prevalence of the mutation increased with increasing serum glucose levels (test for trend P < .005). We conclude that the Met-985 insulin-receptor variant associates with hyperglycemia and represents a risk factor for NIDDM.