Separation of biologically active chromium-containing complexes from yeast extracts and other sources of glucose tolerance factor (GTF) activity

A procedure has been developed, based on ion-exchange chromatography, that readily allows the separation of eleven apparently homogeneous chromium-containing fractions from a brewer's yeast extract. Four of the fractions are amphoteric and show no glucose tolerance factor (GTF) activity, three are classified as negative (two of which are biologically inactive, while the third one shows a slight degree of GTF activity), whereas the four cationic chromium-containing fractions all show varying degrees of GTF activity. Application of the separation procedure to other biological sources of GTF activity resulted in a spectrum of cationic fractions, over the pH range 1.75 to 12, which suggests that GTF cannot be a single species. The cationic chromium-containing fraction from pork kidney powder and fraction P-3 from yeast appear to contain the most GTF-active material and P-3 shows saturation kinetics as expected for a biologically significant substance.     

Heat tolerance in rats following administration of streptozotocin,glucose, insulin and glucose plus insulin

Rise in rectal temperature (T_re) and survival time was determined on exposure to 38°C in adult normoglycemic and diabetic (streptozotocin treated) rats and 1 h following glucose feeding or insulin administration or both, and in young rats with and without glucose feeding or insulin treatment. The heat tolerance of adult animals treated with streptozotocin and insulin plus glucose and of adult and young animals treated with glucose feeding or insulin was less than that of their respective normoglycemic controls. The rectal temperature on exposure to heat in the treated animals was significantly higher than that of controls in the adult, but not in young rats. Exposure to heat of the normoglycemic and glucose-fed animals resulted in a rise in blood glucose in the adults and a fall in the young. The already raised blood glucose level in the streptozotocin-treated animals rose further on exposure to heat. The rate of recovery of the blood glucose was not significantly altered by exposure of the animals to heat 60 min after administration of insulin or insulin plus glucose.     

Cold tolerance in rats following administration of streptozotocin,glucose, insulin and glucose plus insulin

Fall in rectal temperature (T_re) and survival time was determined on exposure to–20°C in adult normoglycemic and diabetic (streptozotocin treated) rats and 1 h following glucose feeding or insulin administration or both and on exposure to–10°C in young rats with and without glucose feeding. The susceptibility to frostbite was determined by exposure of the limbs to freezing mixture of–19°C or–23°C. The rate of fall of T_re was less and the survival time more in glucose and insulin plus glucose treated animals. On the other hand, the rate of fall of T_re was more and the survival time less, in dia betic and insulin-treated animals. The rectal temperature at which the animal died was the same in the control and the treated animals. The susceptibility to frost bite was more in insulin treated and diabetic animals and less in glucose-fed animals. Exposure to cold during the second h after glucose or glucose plus insulin injection did not alter the blood glucose from that obtained at room temperature. In insulin-treated animals the rate of rise of blood glucose during the second h was much higher at low temperature than at room temperature. The rise in blood glucose in diabetic animals was much higher than in normoglycemic animals exposed to cold.     

Concentrated loss of insulin secretion in Wistar rats with normal glucose tolerance

Rats with decreased insulin response and with normal glucose tolerance were concentrated by repeated selective breeding of normal Wistar rats with low insulinogenic index. In general, the mean insulinogenic index of the inbred offsprings showed a tendency to decrease more than their parents generation. Thus mean insulinogenic indices in second (F2), third (F3) and fourth (F4) generations were significantly reduced more than the normal rats without glucose intolerance. Pancreatic islets from the F3 and F4 rats lost partially their ability to release insulin at 20 mM glucose in vitro. It is suggested that a defect responsible for the decreased insulin response in the F2, F3 and F4 rats resulted from a loss of the ability to secrete insulin in each islet, and that this defect was concentrated by repeated selective breeding of normal Wistar rats.     

Interaction of a newly isolated intestinal polypeptide (PHI) with glucose and arginine to effect the secretion of insulin and glucagon

A newly isolated porcine intestinal polypeptide (PHI) at a concentration of 3 ng/ml induced insulin release from isolated perfused rat pancreas at basal (4.4 mmol/1) as well as at increased (16.7 mmol/1) glucose levels. Furthermore, the peptide enhanced arginine-stimulated glucagon secretion, but did not effect arginine-stimulated insulin release.     

Erythrocyte insulin receptor and glucose tolerance test in children treated with prednisolone

Insulin receptors of erythrocytes and oral glucose tolerance test (O-GTT) were investigated in sixteen children treated with prednisolone for various diseases. Ten patients (Group 1) received low doses of prednisolone (0.2-0.5 mg/kg body weight/day) and six patients (Group 2) received higher doses of prednisolone (1.5-2.0 mg/kg body weight/day). Compared to the values for controls, the sums of blood glucose (sigma BS) at O-GTT in both group 1 and group 2 patients were significantly elevated. (422 +/- 75 mg/dl, p less than 0.01 Group 1; 419 +/- 39 mg/dl, p less than 0.01 Group 2; 338 +/- 41 mg/dl controls) Significant differences were not observed in the sums of insulin concentration at O-GTT, fasting blood concentration and basal insulin levels among these two groups and the controls. There was a significant increase in the maximum insulin binding in group 2 (9.13 +/- 0.68% in group 2, 7.97 +/- 1.06% in controls, p less than 0.05), but not in group 1 (8.59 +/- 1.82%). There is no significant difference in binding affinity or the number of receptors between any of these two patients' groups and the controls. When patients in group 1 and group 2 were combined, sigma IRI levels were significantly elevated in the patients (p less than 0.05). These results suggested that prednisolone treatment with a smaller dosage as well as with the higher dosage resulted in a carbohydrate intolerance, the main cause of which is located in a postreceptor step (or steps) of insulin action.     

Interaction between insulin (VNTR) and hepatic lipase (LIPC-514C>T) variants on the response to an oral glucose tolerance test in the EARSII group of young healthy men

Insulin resistance is polygenic in origin, and can be observed at an early age. We have shown that variations in APOC3-482T>C and hepatic lipase (LIPC)-514C>T), individually (APOC3 alone) and interactively, modulate insulin and glucose levels after an OGTT in young healthy men participating in the European Atherosclerosis Research Study II (EARSII). Variation in the insulin gene (INS) variable number tandem repeat (VNTR) has been found to predispose to type 1 and type 2 diabetes. We have evaluated the HphI site 23 bp upstream of the INS gene (a surrogate marker for the VNTR) in EARSII (n=822), to determine if variation in INS contributes to insulin resistance. Carriers of the INS VNTR class III (HphI-) allele (frequency=0.29 (95%CI 0.27, 0.31)) had significantly higher 60-min insulin concentrations after the OGTT (P=0.014) and a marginally higher AUC insulin (P=0.07), compared to class I (HphI+) homozygotes. However, this effect on AUC insulin was modified by the level of physical activity, displaying significant gene:environment interaction (P=0.03). We tested for gene:gene interaction between the INS VNTR and both the LIPC-514C>T and APOC3-482T>C. While there was a significant interaction between INS VNTR and LIPC-514C>T on AUC glucose (P=0.013) and on AUC insulin (P=0.015), there was no interaction with APOC3-482T>C. Thus, despite a modest effect of the INS VNTR alone, the influence of this variant on insulin sensitivity was modified by gene:environment and gene:gene interactions, illustrating the biological complexity of insulin resistance.     

Effects of secretin on insulin secretion and glucose tolerance.

Effects of intravenous (IV) infusion of secretin during IV infusion of glucose were examined in normal men. Secretin was administered according to three schedules: with each schedule a comparable priming dose was delivered in the first minute, but this was followed by a maintained (120 min) infusion of secretin at a relatively high rate, or by maintained infusion at one-third that rate, or by brief (15 min) infusion at the lower rate. The lower infusion rate produced increments in secretin in the blood within the range attainable during endogenous secretion. By comparison with effects of glucose alone each secretin infusion enhanced the increments of immunoreactive insulin in the blood. Enhancement of the early release (0-5 min) of insulin was similar with each type of secretin infusion, but the integrated changes in insulin levels through the total infusion period were related to the total doses of secretin. With each dose of secretin glucose tolerance was improved but the three mean glucose curves observed during infusions of secretin were not distinguishable from one another in spite of widely different integrated insulin responses. Secretin did not modify suppression of immunoreactive glucagon or free fatty acids in the blood during hyperglycemia. The results suggest that the effect of continuous administration of secretin on glucose tolerance is not simply related to its integrated insulinotropic action. It is suggested that the effect may be highly dependent on enhancement of insulin secretion early in the response to glycemia, or that it may be due to effects of secretin on glucose production or disposal which are not mediated by insulin.     

Enhanced glucose tolerance in pancreatic-derived factor (PANDER) knockout C57BL/6 mice

Pancreatic-derived factor (PANDER; also known as FAM3B) is a uniquely structured protein strongly expressed within and secreted from the endocrine pancreas. PANDER has been hypothesized to regulate fasting and fed glucose homeostasis, hepatic lipogenesis and insulin signaling, and to serve a potential role in the onset or progression of type 2 diabetes (T2D). Despite having potentially pivotal pleiotropic roles in glycemic regulation and T2D, there has been limited generation of stable animal models for the investigation of PANDER function, and there are no models on well-established genetic murine backgrounds for T2D. Our aim was to generate an enhanced murine model to further elucidate the biological function of PANDER. Therefore, a pure-bred PANDER knockout C57BL/6 (PANKO-C57) model was created and phenotypically characterized with respect to glycemic regulation and hepatic insulin signaling. The PANKO-C57 model exhibited an enhanced metabolic phenotype, particularly with regard to enhanced glucose tolerance. Male PANKO-C57 mice displayed decreased fasting plasma insulin and C-peptide levels, whereas leptin levels were increased as compared with matched C57BL/6J wild-type mice. Despite similar peripheral insulin sensitivity between both groups, hepatic insulin signaling was significantly increased during fasting conditions, as demonstrated by increased phosphorylation of hepatic PKB/Akt and AMPK, along with mature SREBP-1 expression. Insulin stimulation of PANKO-C57 mice resulted in increased hepatic triglyceride and glycogen content as compared with wild-type C57BL/6 mice. In summary, the PANKO-C57 mouse represents a suitable model for the investigation of PANDER in multiple metabolic states and provides an additional tool to elucidate the biological function and potential role in T2D.KEY WORDS: Pancreatic-derived factor, FAM3B, Knockout model, Glycemic regulation, Hepatic insulin signaling, Glucose tolerance     

Prolactin release in liver cirrhosis with impaired glucose tolerance (IGT)

The effects of acute TRH and cimetidine administration on the plasma prolactin (PRL) response have been studied in cirrhotic patients with impaired glucose tolerance (IGT). I v. TRH administration stimulates PRL release both in cirrhotics and controls; i.v. cimetidine did not induced a significant rise of PRL in liver cirrhosis. Present findings demonstrate that PRL is not responsible for the deterioration of glucose handling in alcoholic cirrhotic patients examined.     

Insulin-like growth factor I and impaired glucose tolerance

The effects of circulating insulin-like growth factor I (IGF-I) on glucose metabolism are well recognized. IGF-I is also important in maintaining beta-cell mass and regulating endogenous growth hormone (GH) levels. Low IGF-I levels could explain links between small birth size and the risk of developing type 2 diabetes mellitus in short, obese adults. In a recent prospective study, childhood insulin secretion was related to IGF-I levels and statural growth, whereas insulin sensitivity was related to early post-natal weight gain. Common genetic polymorphisms in the IGF1 gene have been linked to small birth size, post-natal growth and future diabetes risk, but these results have been inconsistent. Recent adult studies have demonstrated that lower baseline IGF-I levels predict the subsequent development of impaired glucose tolerance (IGT), type 2 diabetes and cardiovascular disease. Administration of low-dose GH therapy, at a dose that minimizes the lipolytic effects of GH and has the ability to increase IGF-I levels, enhances insulin sensitivity in young healthy adults and in GH-deficient adults and increases insulin secretion in individuals with IGT. Whether the administration of low-dose GH, recombinant IGF-I or combined IGF-I/IGF-binding protein 3 therapy prevents future development of IGT or type 2 diabetes in high-risk normoglycaemic and GH-deficient individuals merits further long-term studies.     

A newly synthetic chromium complex--chromium(phenylalanine)3 improves insulin responsiveness and reduces whole body glucose tolerance

Low-molecular-weight organic chromium complexes such as chromium picolinate are often used as dietary supplements to improve insulin sensitivity and to correct dyslipidemia. However, toxicity associated with such chromium compounds has compromised their therapeutic value. The aim of this study was to evaluate the impact of a newly synthesized complex of chromium with phenylalanine, Cr(pa)3 on insulin-signaling and glucose tolerance. Cr(pa)3 was synthesized by chelating chromium(III) with D-phenylalanine ligand in aqueous solution. In mouse 3T3-adipocytes, Cr(pa)3 augmented insulin-stimulated glucose-uptake as assessed by a radioactive-glucose uptake assay. At the molecular level, Cr(pa)3 enhanced insulin-stimulated phosphorylation of Akt in a time- and concentration-dependent manner without altering the phosphorylation of insulin receptor. Oral treatment with Cr(pa)3 (150 microg/kg/d, for six weeks) in ob/ob+/+ obese mice significantly alleviated glucose tolerance compared with untreated obese mice. Unlike chromium picolinate, Cr(pa)3 does not cleave DNA under physiological reducing conditions. Collectively, these data suggest that Cr(pa)3 may represent a novel, less-toxic chromium supplement with potential therapeutic value to improve insulin sensitivity and glycemic control in type II diabetes.     

The effects of postprandial glucose and insulin levels on postprandial endothelial function in subjects with normal glucose tolerance

ABSTRACT: BACKGROUND: Previous studies have demonstrated that postprandial hyperglycemia attenuates brachial artery flow-mediated dilation (FMD) in prediabetic patients, in diabetic patients, and even in normal subjects. We have previously reported that postprandial hyperinsulinemia also attenuates FMD. In the present study we evaluated the relationship between different degrees of postprandial attenuation of FMD induced by postprandial hyperglycemia and hyperinsulinemia and differences in ingested carbohydrate content in non-diabetic individuals. METHODS: Thirty-seven healthy subjects with no family history of diabetes were divided into 3 groups: a 75-g oral glucose loading group (OG group) (n = 14), a test meal group (TM group) (n = 12; 400 kcal, carbohydrate content 40.7 g), and a control group (n = 11). The FMD was measured at preload (FMD0) and at 60 minutes (FMD60) and 120 (FMD120) minutes after loading. Plasma glucose (PG) and immunoreactive insulin (IRI) levels were determined at preload (PG0, IRI0) and at 30 (PG30, IRI30), 60 (PG60, IRI60), and 120 (PG120, IRI120) minutes after loading.ResultPercentage decreases from FMD0 to FMD60 were significantly greater in the TM group ([MINUS SIGN]21.19 % [PLUS-MINUS SIGN] 17.90 %; P < 0.001) and the OG group ([MINUS SIGN]17.59 % [PLUS-MINUS SIGN] 26.64 %) than in the control group (6.46 % [PLUS-MINUS SIGN] 9.17 %; P < 0.01), whereas no significant difference was observed between the TM and OG groups. In contrast, the percentage decrease from FMD0 to FMD120 was significantly greater in the OG group ([MINUS SIGN]18.91 % [PLUS-MINUS SIGN] 16.58 %) than in the control group (6.78 % [PLUS-MINUS SIGN] 11.43 %; P < 0.001) or the TM group (5.22 % [PLUS-MINUS SIGN] 37.22 %; P < 0.05), but no significant difference was observed between the control and TM groups. The FMD60 was significantly correlated with HOMA-IR (r = [MINUS SIGN]0.389; P < 0.05). In contrast, FMD120 was significantly correlated with IRI60 (r = [MINUS SIGN]0.462; P < 0.05) and the AUC of IRI (r = [MINUS SIGN]0.468; P < 0.05). Furthermore, the percentage change from FMD0 to FMD120 was significantly correlated with the CV of PG (r = 0.404; P < 0.05), IRI60 (r = 0.401; p < 0.05) and the AUC of IRI (r = 0.427; P < 0.05). No significant correlation was observed between any other FMDs and glucose metabolic variables. CONCLUSION: Differences in the attenuation of postprandial FMD induced by different postprandial insulin levels may occur a long time postprandially but not shortly after a meal.