Clearance of apoptotic beta-cells is reduced in neonatal autoimmune diabetes-prone rats.

The kinetics of beta-cell death in neonatal diabetes-prone (BBdp) and diabetes-resistant (BBdr) BioBreeding rats was investigated using both direct (histochemical) and indirect (mathematical modelling) techniques. In both BBdp and BBdr rats, the incidence of TUNEL positive beta-cells increased until 10 days of age before declining. The number of apoptotic beta-cells was significantly higher in BBdp as compared to BBdr neonates from birth until 20 days of age (P<0.05). Using a mathematical model applied to the time course of beta-cell mass and replication rate, a wave of net beta-cell loss was detected between 10 and 20 days of age in both strains. In contrast to the observed difference in the incidence of TUNEL positive beta-cells, with the model-based approach we found no difference in the rate of beta-cell apoptosis between BBdp and BBdr rats prior to weaning. As the number of apoptotic cells present in a tissue depends on the rate at which cells die and the rate at which the apoptotic cell debris is cleared, we compared in vitro phagocytosis of apoptotic thymocytes by peritoneal macrophages from 2-week-old BBdp and BBdr rats. Macrophages from BBdp neonates engulfed significantly less apoptotic cells as compared to BBdr neonates (P<0.0005). Taken together, these findings suggest that there is impaired clearance of apoptotic beta-cells in diabetes-prone BB rats during the neonatal period.

Long-term treatment with the dipeptidyl peptidase IV inhibitor P32/98 causes sustained improvements in glucose tolerance, insulin sensitivity, hyperinsulinemia, and beta-cell glucose responsiveness in VDF (fa/fa) Zucker rats.

The incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are responsible for >50% of nutrient-stimulated insulin secretion. After being released into the circulation, GIP and GLP-1 are rapidly inactivated by the circulating enzyme dipeptidyl peptidase IV (DP IV). The use of DP IV inhibitors to enhance these insulinotropic hormonal axes has proven effective on an acute scale in both animals and humans; however, the long-term effects of these compounds have yet to be determined. Therefore, we carried out the following study: two groups of fa/fa Zucker rats (n = 6 each) were treated twice daily for 3 months with the DP IV inhibitor P32/98 (20 mg.kg(-1).day(-1), p.o.). Monthly oral glucose tolerance tests (OGTTs), performed after drug washout, revealed a progressive and sustained improvement in glucose tolerance in the treated animals. After 12 weeks of treatment, peak OGTT blood glucose values in the treated animals averaged 8.5 mmol/l less than in the controls (12.0 +/- 0.7 vs. 20.5 +/- 1.3 mmol/l, respectively). Concomitant insulin determinations showed an increased early-phase insulin response in the treated group (43% increase). Furthermore, in response to an 8.8 mmol/l glucose perfusion, pancreata from controls showed no increase in insulin secretion, whereas pancreata from treated animals exhibited a 3.2-fold rise in insulin secretion, indicating enhanced beta-cell glucose responsiveness. Also, both basal and insulin-stimulated glucose uptake were increased in soleus muscle strips from the treated group (by 20 and 50%, respectively), providing direct evidence for an improvement in peripheral insulin sensitivity. In summary, long-term DP IV inhibitor treatment was shown to cause sustained improvements in glucose tolerance, insulinemia, beta-cell glucose responsiveness, and peripheral insulin sensitivity, novel effects that provide further support for the use of DP IV inhibitors in the treatment of diabetes.

Effect of glucagon-like peptide 1 on non-insulin-mediated glucose uptake in the elderly patient with diabetes.

An important cause of elevated glucose levels in elderly patients with diabetes is an alteration in non-insulin-mediated glucose uptake (NIMGU). Glucagon-like peptide 1 (GLP-1) is an intestinal insulinotropic hormone. It has been proposed that this hormone also lowers glucose levels by enhancing NIMGU. This study was conducted to determine whether GLP-1 augments NIMGU in elderly patients with diabetes, a group in which NIMGU is known to be impaired. Studies were conducted on 10 elderly patients with type 2 diabetes (aged 75 +/- 2 years, BMI 27 +/- 1 kg/m(2)) who underwent paired 240-min glucose clamp studies. In each study, octreotide was infused to suppress endogenous insulin release, and tritiated glucose methodology was used to measure glucose production and disposal rates. For the first 180 min, no glucose was infused. From 180 to 240 min, glucose was increased to 11 mmol/l using the glucose clamp protocol. In the GLP-1 study, GLP-1 was infused from 30 to 240 min. In a subsequent control study, insulin was infused using the glucose clamp protocol from 30 to 240 min to match the insulin levels that occurred during the GLP-1 infusion study. During hyperglycemia, GLP-1 enhanced glucose disposal (control study: 2.52 +/- 0.19 mg x kg(-1) x min(-1); GLP-1 study: 2.90 +/- 0.17 mg x kg(-1) x min(-1); P < 0.0001). Hepatic glucose output was not different between studies. We conclude that GLP-1 may partially reverse the defect in NIMGU that occurs in elderly patients with diabetes.

Dietary P(i) deprivation in rats affects liver cAMP, glycogen, key steps of gluconeogenesis and glucose production.

We previously reported [Xie, Li, Méchin and van de Werve (1999) Biochem. J. 343, 393-396] that dietary phosphate deprivation for 2 days up-regulated both the catalytic subunit and the putative glucose-6-phosphate translocase of the rat liver microsomal glucose-6-phosphatase system, suggesting that increased hepatic glucose production might be responsible for the frequent clinical association of hypophosphataemia and glucose intolerance. We now show that liver cAMP was increased in rats fed with a diet deficient in P(i) compared with rats fed with a control diet. Accordingly, in the P(i)-deficient group pyruvate kinase was inactivated, the concentration of phosphoenolpyruvate was increased and fructose 2, 6-bisphosphate concentration was decreased. Phosphoenolpyruvate carboxykinase activity was marginally increased and glucokinase activity was unchanged by P(i) deprivation. The liver glycogen concentration decreased in the P(i)-deficient group. In the fed state, plasma glucose concentration was increased and plasma P(i) and insulin concentrations were substantially decreased in the P(i)-deficient group. All of these changes, except decreased plasma P(i), were cancelled in the overnight fasted P(i)-deficient group. In the fasted P(i)-deficient group, immediately after a glucose bolus, the plasma glucose level was elevated and the inhibition of endogenous glucose production was decreased. However, this mild glucose intolerance was not sufficient to affect the rate of fall of the glucose level after the glucose bolus. Taken together, these changes are compatible with a stimulation of liver gluconeogenesis and glycogenolysis by the P(i)-deficient diet and further indicate that the liver might contribute to impaired glucose homeostasis in P(i)-deficient states.

A comparison of the effects of n-3 fatty acids from linseed oil and fish oil in well-controlled type II diabetes.

OBJECTIVE: Supplementation of type II diabetic diets with n-3 fatty acids (FAs) from fish oil (FO) has been associated with lowered triglyceride and VLDL levels, although reports of impaired glycemic control have limited their use. Effects of n-3FAs from nonmarine sources are less well documented. Therefore, an investigation comparing the effects of linseed oil (LO) with FO supplementation was undertaken in subjects with type II diabetes. RESEARCH DESIGN AND METHODS: Eleven subjects with type II diabetes were given supplements with LO and FO for 3 months each in a randomized double-blind crossover fashion after 3 months of olive oil placebo. Oils were given as 35 mg FA.kg body wt-1.day-1. After each 3-month period, fasting glucose and insulin levels, HbA1c, lipid profiles, insulin sensitivity (SI), glucose effectiveness (SG), and acute insulin response to glucose (AIRG) were evaluated. RESULTS: HbA1c and lipid values were within the normal range at randomization. Repeated measures analysis of variance testing found no significant differences in weight; fasting glucose and insulin levels; HbA1c; total, LDL, and HDL cholesterol levels; SI; SG; or AIRG with either active oil. FO was associated with significant reductions in triglycerides and a trend toward decreased SI. CONCLUSIONS: In a population with well-controlled type II diabetes, 3 months of FO but not LO resulted in lowered triglyceride levels. Neither LO nor FO significantly affected glycemic control, cholesterol values, SG, or insulin secretion, while a nonsignificant trend toward decreased insulin sensitivity was found with FO.

Beta-cell dysfunction independent of obesity and glucose intolerance in the polycystic ovary syndrome.

Several distinct groups of subjects at high risk to develop noninsulin-dependent diabetes mallitus (NIDDM) have been found to have insulin secretory defects when beta-cell function is assessed in the context of peripheral insulin sensitivity. We investigated this with a modified frequently sampled iv glucose tolerance test to determine acute insulin responses to glucose (AIRg) as well as insulin action by minimal model analysis in 28 women with polycystic ovary syndrome (PCOS; 15 obese and 13 nonobese) and 29 age- and weight-matched normal women (14 obese and 15 nonobese). No subject, PCOS or control, had fasting hyperglycemia, but seven PCOS women (six obese and one nonobese) had impaired glucose tolerance or NIDDM. The PCOS women had significantly decreased insulin sensitivity compared to the normal women (P < or = 0.001), and the obese women were less sensitive than the nonobese women (P < or = 0.001). The empiric measure of insulin release, AIRg, was significantly increased by obesity (P < or = 0.01), but not by PCOS. However, the disposition index (insulin sensitivity x AIRg) was significantly decreased by both PCOS (< or = 0.005) and obesity (< or = 0.005), suggesting that AIRg was inadequate for the degree of insulin resistance. When the PCOS women with impaired glucose tolerance or NIDDM were removed from the analysis, all of the reported PCOS-related changes in insulin action and secretion remained significant. We conclude that both obese and nonobese PCOS women have beta-cell dysfunction as well as insulin resistance. However, this was not associated with glucose intolerance in the majority of PCOS women.

Gender differences in the metabolic response to graded numbers of transplanted islets of Langerhans.

Gender differences after treatment with streptozotocin (STZ) have been previously reported; however, differences in the glucose response to islet transplantation in STZ-induced diabetes in male and female rats after islet transplantation have not been examined. Male and female Wistar-Furth rats were made diabetic using STZ (55 mg/kg BW) and then given an intraportal islet transplant. Control animals received sham injections and sham transplant surgery; diabetic animals received STZ and sham surgery. In male animals, islet grafts contained 0 (diabetic), 250, 500, 1000, 1500, 2000, and 3000 islets; in female rats, grafts were made up of 0, 500 700, 750, 1000, or 2500 islets. STZ treatment had more dramatic effects on male than female rats. During the diabetic phase, body weights of male rats were significantly reduced compared to those of control male animals; this was not observed among females. Although all STZ-treated animals were hyperglycemic, plasma glucose levels in male diabetic rats were significantly higher than those in females during this phase (29.8 +/- 2.1 vs. 24.6 +/- 0.6 mM). After islet transplantation, body weight gain was positively associated with the number of islets transplanted in male rats (r2 = 0.59; P < 0.01), but not in females (r2 = 0.09; P > 0.8). In both male and female rats, animals that received 1000 islets or more were generally normoglycemic by 3 weeks posttransplant (males, 10.8 +/- 2.2 mM; females, 7.1 +/- 0.2 mM). Approximately 60% of male and female animals that received 500 islets achieved a reduction in plasma glucose levels. Mean plasma glucose levels were 17.2 +/- 2.3 in the females and 22.6 +/- 1.0 mM in males. However, a significantly larger proportion of female 500-islet animals (6 of 16) achieved a plasma glucose level of 9.5 mM or less compared with males receiving 500 islets (2 of 30). Multivariate regression analysis suggests that sex and islet number interact to affect glycemic normalization after islet transplantation. Gender differences appear to influence body weight and plasma glucose responses to islet transplantation. This finding may have particular relevance when a marginal number of functional islets are available.

Polycystic ovary syndrome: lack of hypertension despite profound insulin resistance.

It has been hypothesized that insulin resistance and hyperinsulinemia contribute to the development of arterial hypertension. To further investigate this relationship, we compared arterial blood pressure in controls and women with polycystic ovary syndrome (PCO), an insulin-resistant state. Fourteen PCO women and 18 normal control women of similar age, body mass index, and race were studied. Plasma glucose and insulin levels were determined in an oral glucose tolerance test. The insulin sensitivity (SI) index was determined by the minimal model method. Systolic and diastolic blood pressure were measured by 24-h ambulatory monitoring. Left ventricular mass was assessed by echocardiography. The two groups had comparable fasting glucose levels, but the 2-h postload glucose was higher in PCO (8.0 +/- 0.5 vs. 5.6 +/- 0.3 mmol/L; P less than 0.001). Compared to controls, PCO women were significantly more insulin resistant by fasting insulin, 2-h insulin concentrations, and SI (28.3 +/- 6.7 vs. 68.3 +/- 10.0 min-1/nmol.mL; P less than 0.01). Average ambulatory systolic (121 +/- 2 vs. 118 +/- 2 mm Hg) and diastolic (76 +/- 2 vs. 73 +/- 2 mm Hg) blood pressures were similar for PCO and control women. No difference was found in left ventricular mass. Therefore, despite profound insulin resistance and hyperinsulinemia, women with PCO do not have increased arterial pressure or left ventricular mass.

Androgen response to endogenous insulin secretion during the frequently sampled intravenous glucose tolerance test in normal and hyperandrogenic women.

Women with ovarian hyperandrogenism frequently have insulin resistance, whose underlying mechanism remains to be determined. In the present study we have investigated the relationship between insulin sensitivity and the acute effect of endogenous insulin secretion on circulating androgen levels. Insulin sensitivity, glucose-mediated insulin release, and glucose/insulin-stimulated androgen responses were determined during a frequently sampled iv glucose tolerance test in a group of 19 women with clinical evidence of polycystic ovary syndrome (PCOS) and 9 age- and weight-matched controls. Insulin (I), glucose, androstenedione, testosterone (T), free T, and dehydroepiandrosterone (DHEA) levels were measured before and during the 3 h following iv administration of glucose (300 mg/kg). Intravenous tolbutamide (300-500 mg) was injected 20 min after the glucose injection. Insulin sensitivity (SI) was calculated by application of the minimal model of glucose kinetics. Fasting androstenedione, T, free T, and I concentrations were significantly higher in the women with PCOS than in controls (P less than 0.02). In PCOS subjects, fasting I was correlated with both T (r = 0.51; P less than 0.05) and DHEA (r = 0.706; P less than 0.01). SI was significantly lower in PCOS subjects [SI, 68.35 +/- 8.34 min-1/(nmol/mL] than in control subjects (SI, 133.36 +/- 21.7 min-1/(nmol/mL)]. A significant decline in DHEA levels was observed in control subjects 3 h after glucose administration (from 28.4 +/- 3.0; final, 16.2 +/- 2.4; P less than 0.02). PCOS women with normal insulin sensitivity [SI, greater than 75.0 min-1/(nmol/mL)] showed a similar fall in DHEA (from 20.3 +/- 2.5 to 12.8 +/- 1.8 nmol/L; P less than 0.02). No significant change occurred in insulin-resistant PCOS subjects [SI, less than 75.0 min-1/(nmol/mL)]. Other androgen levels showed a modest nonsignificant decline during the study in PCOS and control groups. These findings confirm the weight-independent insulin resistance of some hyperandrogenic women. The failure of glucose-stimulated endogenous insulin secretion to significantly depress DHEA levels in insulin-resistant women with PCOS may account in part for their androgen excess.

Glucoregulatory response to moderate exercise in long-term islet cell autografted dogs.

The glucoregulatory response to moderate treadmill exercise (approximately 60% maximum heart rate; 60 min at 100 m/min, 12% grade) was examined in six controls and six pancreatectomized dogs that had been normoglycemic and insulin independent for more than 1 year since autograft of isolated islets of Langerhans (Tx). There were no significant intergroup differences in plasma glucose levels during exercise, but return to baseline after exercise was delayed in Tx (p less than 0.05). In Tx, the initially suppressed insulin levels rose above baseline from 30 to 60 min. Within Tx, exercise-induced levels of plasma glucagon and epinephrine were more variable than control and strongly correlated (r = 0.81, p less than 0.001), perhaps indicating that the A cells within the grafted islets were regulated by circulating beta-adrenergic agonists. We conclude that the isolated islets were removed from direct central control. In Tx dogs, the variable counterregulatory responses and the diminished recovery of plasma glucose after exercise indicate reliance on alternative glucoregulatory mechanisms.

Extrapancreatic effect of somatostatin infusion to increase glucose clearance.

Constant intraportal insulin, coupled with variable intraportal glucagon, was used in the attempt to reestablish basal metabolic conditions in dogs during somatostatin (SRIF) infusion (0.8 micrograms X min-1 X kg-1). SRIF alone lowered glucose (G), insulin (I), and glucagon (GN) (G: 90 +/- 5 to 69 +/- 1 mg/dl; I: 18 +/- 4 to 4 +/- 1 microU/ml; GN: 257 +/- 52 to 168 +/- 40 pg/ml; P less than 0.05 or better). Hormone replacement. Hypoglycemia persisted (G at steady state, SS, 60-150 min): 12 +/- 3 mg/dl below basal; P = 0.006) despite intraportal insulin replacement (200 microU X min-1 X kg-1; insulin at basal: 14 +/- 1; at SS: 14 +/- 2 microU/ml; P greater than 0.9) and glucagon overreplacement (basal: 341 +/- 42; SS: 486 +/- 80 pg/ml; P less than 0.05). Glucose clearance was increased 65% above basal (P less than 0.0001). Insulin underreplacement. With a lower intraportal insulin infusion rate (50 microU X min-1 X kg-1), insulin fell from basal (10 +/- 2 microU/ml) to 4 +/- 1 microU/ml during steady state (P = 0.03). Glucose and glucose clearance were normalized to basal values (G: 85 +/- 3 mg/dl, P = 0.3; clearance: 5.7 +/- 0.5 ml X min-1 X kg-1; P = 0.2) with full glucagon replacement (basal: 281 +/- 120; SS: 264 +/- 80 pg/ml; P greater than 0.9). Thus, during constant SRIF infusion, normoglycemia was reattained when insulin was underreplaced via the portal vein. The failure to reattain euglycemia with normoinsulinemia was due to a SRIF-induced increase in extrahepatic glucose clearance. Insulin replacement and growth hormone (GH) infusion. GH (15 ng X min-1 X kg-1) partially reversed the hypoglycemia during SRIF, with full insulin replacement. The SRIF-induced increase in glucose clearance may be partially mediated by a decrease in GH.