Sitagliptin improves beta-cell function in patients with acute coronary syndromes and newly diagnosed glucose abnormalities--the BEGAMI study.

BACKGROUND: Newly detected impaired glucose tolerance (IGT) or type 2 diabetes mellitus (T2DM) are common in patients with acute coronary syndrome (ACS; i.e. unstable angina/myocardial infarction) and related to disturbed beta-cell function. The aim of this study is to test the hypothesis that treatment with a dipeptidyl peptidase-4 inhibitor initiated soon after a coronary event improves beta-cell function. METHODS: Acute coronary syndrome ACS patients with IGT or T2DM (n = 71), screened by oral glucose tolerance test (OGTT) 4-23 days (median 6 days) after hospital admission, were randomly assigned to sitagliptin 100 mg (n = 34) or placebo (n = 37) and treated for a duration of 12 weeks. All patients received lifestyle advice but no glucose-lowering agents other than the study drug. The study end-point was beta-cell function assessed using the insulinogenic index (IGI = ΔInsulin30 /ΔGlucose30 ), derived from an OGTT, and acute insulin response to glucose (AIRg) assessed by a frequently sampled intravenous glucose tolerance test. RESULTS: The IGI and AIRg did not differ at baseline between the sitagliptin and placebo groups (69.9 vs. 66.4 pmol mmol(-1) and 1394 vs. 1106 pmol L(-1) min(-1) respectively). After 12 weeks, the IGI was 85.0 in the sitagliptin and 58.1 pmol/mmol in the placebo group (P = 0.013) and AIRg was 1909 and 1043 pmol L(-1) min(-1) (P < 0.0001) in the sitagliptin and placebo groups respectively. Fasting glucose at baseline was 6.1 mmol L(-1) in sitagliptin-treated patients and 6.0 mmol L(-1) in those who received placebo compared with 5.8 and 5.9 mmol L(-1) respectively, after 12 weeks of treatment. Post load glucose metabolism improved in significantly more sitagliptin-treated patients compared with the placebo group (P = 0.003). Sitagliptin was well tolerated. CONCLUSION: Sitagliptin improved beta-cell function and glucose perturbations in patients with ACS and newly diagnosed glucose disturbances.

Low serum 25-hydroxyvitamin D level predicts progression to type 2 diabetes in individuals with prediabetes but not with normal glucose tolerance.

AIMS/HYPOTHESIS: Vitamin D deficiency may increase the risk of type 2 diabetes. We therefore investigated whether serum concentrations of 25-hydroxyvitamin D [25(OH)D] would predict the development of prediabetes (impaired fasting glucose, impaired glucose tolerance or the two combined) and type 2 diabetes, either on their own or when combined with serum concentrations of IGF-1 or IGF-binding protein-1 (IGFBP-1), which may interact with 25(OH)D. METHODS: At baseline, participants aged 35-56 years without known type 2 diabetes were examined using OGTTs, 25(OH)D and IGF peptide measurements, and anthropometric and lifestyle data. Participants who had prediabetes or type 2 diabetes at follow-up 8-10 years later were selected as cases; these were then age- and sex-matched to controls with normal glucose tolerance (NGT) at both baseline and follow-up, giving a total of 980 women and 1,398 men. RESULTS: Men but not women in the highest quartile of 25(OH)D level had a decreased OR for developing type 2 diabetes after adjustment for confounders (OR 0.52, 95% CI 0.30, 0.90), an effect accounted for by individuals with prediabetes, but not with NGT, at baseline. In both sexes, progression from prediabetes to type 2 diabetes was reduced by about 25% per 10 nmol/l increase in 25(OH)D. A high IGFBP-1 value was a better predictor of a reduced risk of type 2 diabetes than high 25(OH)D for both sexes, whereas high IGF-1 concentrations predicted a decreased risk only in men. CONCLUSIONS/INTERPRETATION: High serum 25(OH)D concentrations predict a reduced risk of type 2 diabetes in individuals with prediabetes, but not NGT. There were no significant interactions between 25(OH)D and IGFBP-1 or IGF-1 in terms of risk of diabetes. Our data suggest that vitamin D supplementation should be evaluated for the prevention of type 2 diabetes in prediabetic individuals.

The estrogen receptor α-selective agonist propyl pyrazole triol improves glucose tolerance in ob/ob mice: potential molecular mechanisms

The authors and journal apologise for an error in the above paper, which appeared in volume 199 part 2, pages 275­286. The error relates to Fig. 10, given on page 283.

Genetic variation of the adenylyl cyclase 3 (AC3) locus and its influence on type 2 diabetes and obesity susceptibility in Swedish men.

OBJECTIVE: Our previous study using the Goto-Kakizaki rat implicates that the adenylyl cyclase 3 (AC3) is a candidate gene for genetic study of metabolic disorders. The present study aimed to investigate the susceptibility of genetic variation of the AC3 gene in type 2 diabetes (T2D) patients and obese subjects. SUBJECTS AND METHODS: Variation screening in the putative promoter and validation of single nucleotide polymorphisms (SNPs) covering the AC3 gene were performed. In total, 630 Swedish men, including 243 T2D patients (BMI from 18.4 to 45.6 kg m(-2)), 199 obese subjects with normal glucose tolerance (NGT, BMI> or =30 kg m(-2)) and 188 control subjects (NGT, BMI< or =26 kg m(-2)), were genotyped. RESULTS: A novel variant -17A/T in the promoter was identified, but no significant association of this polymorphism with T2D was found. SNPs rs2033655 C/T and rs1968482 A/G were found to be significantly associated with obesity when T2D patients had BMI> or =30 kg m(-2) (P=0.003 and 0.005). The significance was borderline in T2D patients with BMI<30 kg m(-2) (P=0.051 and 0.084) and disappeared in T2D patients with BMI< or =26 kg m(-2). Importantly, analysis in obese subjects with NGT demonstrated that these two polymorphisms were strongly associated with obesity per se (P=0.028 and 0.003). Furthermore, analyses for diplotypes (haplotypic genotypes) predicted an association with BMI in obese subjects. CONCLUSIONS: The present study provides the first evidence that AC3 polymorphisms confer the risk susceptibility to obesity in Swedish men with and without type 2 diabetes.

Psychological distress and risk of pre-diabetes and Type 2 diabetes in a prospective study of Swedish middle-aged men and women.

AIMS: To determine the role of psychological distress as a predictor of pre-diabetes and Type 2 diabetes. METHODS: This cohort study comprised 2127 Swedish middle-aged men and 3100 women with baseline normal glucose tolerance measured by oral glucose tolerance test. At follow-up 8-10 years later, 245 men and 177 women had pre-diabetes [impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and IFG + IGT] and Type 2 diabetes was detected in 103 men and 57 women. Baseline psychological distress was measured by an index of five questions concerning anxiety, apathy, depression, fatigue and insomnia. Odds ratios (ORs) were estimated for pre-diabetes and Type 2 diabetes in association with total psychological distress. In addition, ORs of the single-item questions were calculated. RESULTS: In men, adjusted ORs (95% confidence interval) in the highest index group of psychological distress compared with the lowest group were 1.9 (1.2-2.8) and 2.2 (1.2-4.1) for pre-diabetes and Type 2 diabetes, respectively. Corresponding estimates in women were 1.2 (0.7-2.1) and 0.5 (0.2-1.2). In the middle symptoms groups, adjusted ORs in men were 1.1 (0.8-1.4) for pre-diabetes and 1.2 (0.7-2.0) for Type 2 diabetes and in women 1.8 (1.1-3.0) and 0.7 (0.3-1.4). When analysed separately, the associations with each of the five single factors were similar. CONCLUSIONS: The results indicate that psychological distress, including symptoms of anxiety, apathy, depression, fatigue and insomnia, increases the risk of pre-diabetes and Type 2 diabetes in Swedish middle-aged men. Increased risks were not present in women, except for pre-diabetes in the middle index group.

Mild type II diabetes markedly increases glucose cycling in the postabsorptive state and during glucose infusion irrespective of obesity.

Glucose cycling (GC; G in equilibrium G6P) equals 14% of glucose production in postabsorptive man. Our aim was to determine glucose cycling in six lean and six overweight mild type II diabetics (fasting glycemia: 139 +/- 10 and 152 +/- 7 mg/dl), in postabsorptive state (PA) and during glucose infusion (2 mg/kg per min). 14 control subjects were weight and age matched. GC is a function of the enzyme that catalyzes the reaction opposite the net flux and is the difference between hepatic total glucose output (HTGO) (2-[3H]glucose) and hepatic glucose production (HGP) (6-[3H]-glucose). Postabsorptively, GC is a function of glucokinase. With glucose infusion the flux is reversed (net glucose uptake), and GC is a function of glucose 6-phosphatase. In PA, GC was increased by 100% in lean (from 0.25 +/- 0.07 to 0.43 +/- .08 mg/kg per min) and obese (from 0.22 +/- 0.05 to 0.50 +/- 0.07) diabetics. HGP and HTGO increased in lean and obese diabetics by 41 and 33%. Glucose infusion suppressed apparent phosphatase activity and gluconeogenesis much less in diabetics than controls, resulting in marked enhancement (400%) in HTGO and HGP, GC remained increased by 100%. Although the absolute responses of C-peptide and insulin were comparable to those of control subjects, they were inappropriate for hyperglycemia. Peripheral insulin resistance relates to decreased metabolic glucose clearance (MCR) and inadequate increase of uptake during glucose infusion. We conclude that increases in HGP and HTGO and a decrease of MCR are characteristic features of mild type II diabetes and are more pronounced during glucose infusion. There is also an increase in hepatic GC, a stopgap that controls changes from glucose production to uptake. Postabsorptively, this limits the increase of HGP and glycemia. In contrast, during glucose infusion, increased GC decreases hepatic glucose uptake and thus contributes to hyperglycemia. Obesity per se did not affect GC. An increase in glucose cycling and turnover indicate hepatic insulin resistance that is observed in addition to peripheral resistance. It is hypothesized that in pathogenesis of type II diabetes, augmented activity of glucose-6-phosphatase and kinase may be of importance.

Inhibitory effect of glucagon-like peptide-1 on small bowel motility. Fasting but not fed motility inhibited via nitric oxide independently of insulin and somatostatin.

Effects of glucagon-like peptide-1 (GLP-1)(7-36)amide on fasted and fed motility in the rat small intestine were investigated in relation to its dependence on nitric oxide (NO), insulin, and somatostatin. Small bowel electromyography was performed using bipolar electrodes implanted 15, 25, and 35 cm distal to pylorus, and transit was studied with a radioactive marker. In the fasted state, GLP-1 (5-20 pmol kg-1min-1), reaching physiological plasma levels, prolonged the migrating myoelectric complex (MMC) cycle length along with slowed transit. This effect was antagonized by exendin(9-39)amide. The NO synthase inhibitor Nomega-nitro- L-arginine (L-NNA) also blocked the response to GLP-1, whereas L-arginine restored the response. Insulin (80-200 pmol kg-1min-1) induced irregular spiking, whereas somatostatin (100-500 pmol kg-1min-1) increased the MMC cycle length, independently of NO. In the fed state, GLP-1 (20-40 pmol kg-1min-1) reduced motility, an inhibition unaffected by L-NNA, whereas motility was stimulated by exendin(9-39)amide. Infusion of GLP-1 (20-100 pmol kg-1min-1) did not affect plasma insulin, but somatostatin was increased. In conclusion, GLP-1 seems to inhibit small bowel motility directly via the GLP-1 receptor. Inhibition of fasting motility is dependent of NO and not mediated via insulin or somatostatin, whereas inhibition of fed motility is independent of NO.

Influence of somatostatin on splanchnic glucose metabolism in postabsorptive and 60-hour fasted humans.

Cyclic somatostatin was administered intravenously (10 mug/min for 60 min) to 10 healthy overnight fasted (postabsorptive) subjects and to 5 healthy 60-h fasted subjects. In both groups, arterial insulin and glucagon fell 50% and splanchnic release of these hormones was inhibited. In the overnight fasted subjects splanchnic glucose output fell 70%, splanchnic uptake of lactate and pyruvate was unchanged, alanine uptake fell by 25%, and glycerol uptake rose more than twofold in parallel with an increase in arterial glycerol. In the 60-h fasted group splanchnic glucose output was less than 40% of that observed in the overnight fasted subjects. Somatostatin led to a further decrease (--70%) in glucose production. Splanchnic uptake of lactate and pyruvate fell by 30-40%, amino acid uptake was unchanged, while uptake of glycerol rose fivefold. Total uptake of glucose precursors thus exceeded the simultaneous glucose output by more than 200%. Splanchnic uptake of FFA rose fourfold during somatostatin while output of beta-hydroxybutyrate increased by 75%. Estimated hepatic blood flow fell 25-35% and returned to base line as soon as the somatostatin infusion ended. It is concluded that (a) somatostatin-induced hypoglucagonemia results in inhibition of splanchnic glucose output in glycogen-depleted, 60-h fasted subjects as well as in postabsorptive subjects, indicating an effect of glucagon on hepatic gluconeogenesis as well as glycogenolysis; (b) the glucagonsensitive step(s) in gluconeogenesis affected by somatostatin involves primarily intra-hepatic disposal rather than net hepatic uptake of glucose precursors; (c) splanchnic uptake of fatty acids and ketone output are increased in the face of combined insulin and glucagon deficiency; and (d) diminished splanchnic blood flow may contribute to some of the effects of somatostatin on splanchnic metabolism.

Pancreatic beta cells are important targets for the diabetogenic effects of glucocorticoids.

Abnormalities contributing to the pathogenesis of non-insulin-dependent diabetes mellitus include impaired beta cell function, peripheral insulin resistance, and increased hepatic glucose production. Glucocorticoids are diabetogenic hormones because they decrease glucose uptake and increase hepatic glucose production. In addition, they may directly inhibit insulin release. To evaluate that possible role of glucocorticoids in beta cell function independent of their other effects, transgenic mice with an increased glucocorticoid sensitivity restricted to their beta cells were generated by overexpressing the glucocorticoid receptor (GR) under the control of the insulin promoter. Intravenous glucose tolerance tests showed that the GR transgenic mice had normal fasting and postabsorptive blood glucose levels but exhibited a reduced glucose tolerance compared with their control littermates. Measurement of plasma insulin levels 5 min after intravenous glucose load demonstrated a dramatic decrease in acute insulin response in the GR transgenic mice. These results show that glucocorticoids directly inhibit insulin release in vivo and identify the pancreatic beta cell as an important target for the diabetogenic action of glucocorticoids.

Diabetic Goto-Kakizaki rats display pronounced hyperglycemia and longer-lasting cognitive impairments following ischemia induced by cortical compression.

Hyperglycemia has been shown to worsen the outcome of brain ischemia in several animal models but few experimental studies have investigated impairments in cognition induced by ischemic brain lesions in hyperglycemic animals. The Goto-Kakizaki (GK) rat naturally develops type 2 diabetes characterized by mild hyperglycemia and insulin resistance. We hypothesized that GK rats would display more severe cerebral damage due to hyperglycemia-aggravated brain injury and, accordingly, more severe cognitive impairments. In this study, recovery of motor and cognitive functions of GK and healthy Wistar rats was examined following extradural compression (EC) of the sensorimotor cortex. For this purpose, tests of vestibulomotor function (beam-walking) and combined tests of motor function and learning (locomotor activity from day (D) 1 to D5, operant lever-pressing from D14 to D25) were used. EC consistently reduced cerebral blood flow in both strains. Anesthesia-challenge and EC resulted in pronounced hyperglycemia in GK but not in Wistar rats. Lower beam-walking scores, increased locomotor activity, impairments in long-term habituation and learning of operant lever-pressing were more pronounced and observed at later time-points in GK rats. Fluoro-Jade, a marker of irreversible neuronal degeneration, revealed consistent degeneration in the ipsilateral cortex, hippocampus and thalamus at 2, 7 and 14 days post-compression. The amount of degeneration in these structures was considerably higher in GK rats. Thus, GK rats exhibited marked hyperglycemia during EC, as well as longer-lasting behavioral deficits and increased neurodegeneration during recovery. The GK rat is thus an attractive model for neuropathologic and cognitive studies after ischemic brain injury in hyperglycemic rats.

Socio-economic position at three points in life in association with type 2 diabetes and impaired glucose tolerance in middle-aged Swedish men and women.

BACKGROUND: It has been suggested that low socio-economic position (SEP) during childhood and adolescence predicts risk of adult type 2 diabetes. We investigated the associations between type 2 diabetes and childhood SEP (fathers' occupational position), participants' education and adult SEP (participants' occupational position). To determine possible independent associations between early SEP (fathers' occupational position and participants' education) and disease, we adjusted for adult SEP and factors present in adult life associated with type 2 diabetes. METHODS: This cross-sectional study comprised 3128 men and 4821 women aged 35-56 years. All subjects have gone through a health examination and answered a questionnaire on lifestyle factors. At the health centre, an oral glucose tolerance test was administered and identified 55 men and 52 women with previously undiagnosed type 2 diabetes. Relative risks (RRs) with 95% CIs were calculated in multiple logistic regression analyses. RESULTS: The age-adjusted RRs of type 2 diabetes if having a father with middle occupational position were 2.3 [Confidence interval (CI:1.0-5.1) for women and, 2.0 (CI:0.7-5.6) for men]. Moreover, low education was associated with type 2 diabetes in women, RR = 2.5 (CI:1.2-4.9). Low occupational position in adulthood was associated with type 2 diabetes in women, RR = 2.7 (CI:1.3-5.9) and men, RR = 2.9 (CI:1.5-5.7). The associations between early SEP and type 2 diabetes disappeared after adjustment for adult SEP and factors associated with type 2 diabetes. CONCLUSION: The association between type 2 diabetes and low SEP during childhood and adolescence in middle-aged Swedish subjects disappeared after adjustment for adult SEP and adult risk factors of diabetes.

GHR exon 3 polymorphism: association with type 2 diabetes mellitus and metabolic disorder.

Growth hormone (GH) signaling via the growth hormone receptor (GHR) forms a major part of the GH-IGF-I axis, which is crucial for controlling metabolism and anabolism. Two common variants of the GHR differ by the presence (full length or GHR(fl)) or absence of exon 3 (exon 3 deleted or GHR(d3)), the function of which is unknown. However, differential response to GH treatment has been observed with carriers of the GHR(d3) variant conferring a greater growth rate. This study investigates these GHR variants in subjects with normal glucose tolerance (NGT) and impaired glucose tolerance (IGT), including Type 2 diabetes mellitus (T2DM). DNA was extracted from blood samples from subjects with NGT (n=158), IGT (n=116) and T2DM (n=194). The T2DM subjects in set 1 (n= 39) were newly diagnosed, whilst those in set 2 (n=155) had a mean duration of 7 years. Set 1 also included NGT and IGT subjects. Genotyping by standard PCR and gel electrophoresis were carried out. A significant difference was observed between T2DM and NGT (p<0.0001) with a significantly lower frequency of GHR(d3) in T2DM (3.6% compared to 17% in NGT). Both sets of T2DM subjects with at least one GHR(d3) allele had significantly higher BMI. In the larger subset of T2DM, GHR(d3) was associated with higher CRP levels as well as age adjusted IGF-I, with a trend of higher C-peptide secretion and impaired lipid levels, indicating a phenotype with metabolic disorder when compared to the GHR(fl/fl) T2DM subjects. In conclusion, homozygosity for the GHR(d3) allele appears to be preventive of T2DM. However, when other factors cause overt T2DM, the GHR(d3) allele confers a phenotype indicative of metabolic disorder. This study supports the hypothesis that the two GHR alleles by their inclusion or exclusion of exon 3 are functionally different.

Cysteamine exerts multiple effects on the endocrine cells of the rat pancreas.

We have studied the effects by cysteamine in vitro and in vivo on hormone production and islet cell metabolism in isolated pancreatic islets and perfused pancreas of the rat. In isolated islets, cysteamine dose-dependently depleted somatostatin immunoreactivity by 50% after 60 min exposure to 1 mmol/l of the compound. This effect appeared to be independent of interaction of the drug with secretion of somatostatin from the pancreatic D-cells. Cysteamine, however, interacted acutely not only with the D-cells, but also markedly suppressed glucose-induced insulin release. Moreover, cysteamine inhibited islet glucose oxidation, an effect which reflects interference with the metabolism mainly of the B-cells. The effect of cysteamine on glucose-induced insulin release was prolonged, since it was still observed in the isolated rat pancreas perfused 24 h after in vivo treatment with cysteamine. In contrast to the effects on glucose-induced insulin release, the response to glibenclamide remained unaffected by a previous exposure to cysteamine in vivo. However, both glucose- and glibenclamide-induced somatostatin secretion was reduced by 50%, whereas basal glucagon secretion was significantly enhanced in pancreata from cysteamine-treated rats vs. control rats. We conclude that (1) cysteamine does not specifically affect the D-cells of the islets, and (2) the multiple effects by cysteamine on islet cell function, particularly on B-cell metabolism and secretion, renders the compound unsuitable for the study of paracrine interactions in the islets.

Different domains in the third intracellular loop of the GLP-1 receptor are responsible for Galpha(s) and Galpha(i)/Galpha(o) activation.

It has previously been shown that the GLP-1 receptor is primarily coupled to the adenylate cyclase pathway via activation of Galpha(s) proteins. Recent studies have shown that the third intracellular loop of the receptor is important in the stimulation of cAMP production. We have studied the effect of three synthetic peptide sequences derived from the third intracellular loop of the GLP-1 receptor on signal transduction in Rin m5F cell membranes. The whole third intracellular loop strongly stimulates both pertussis toxin and cholera toxin-sensitive G proteins, while the N-terminal half exclusively stimulates cholera toxin-sensitive G proteins and the C-terminal half only stimulates pertussis toxin-sensitive G-proteins as demonstrated by measurements of GTPase activity. These data confirm that the principal stimulatory G-protein interaction site resides in the third intracellular loop, but also suggest that the GLP-1 receptor is not only coupled to the Galpha(s) but also to the Galpha(i)/Galpha(o) type of G proteins and that distinct domains within the third intracellular loop are responsible for the activation of the different G-protein subfamilies.

Pancreastatin inhibits insulin secretion and stimulates glucagon secretion in mice.

Recently a new peptide, pancreastatin, was isolated from porcine pancreatic extracts. It contains 49 amino acids and shows a structural similarity to chromogranin A, which occurs in secretory granules of the endocrine pancreas. Furthermore, pancreastatin has been found to inhibit glucose-induced insulin secretion in the perfused rat pancreas. However, its effects under in vivo conditions have never been studied. We have therefore investigated the effects of this peptide on insulin and glucagon secretion in vivo in the mouse. We found that an intravenous injection of pancreastatin (4.0 nmol/kg) lowered basal plasma insulin concentration at 6 min from 55 +/- 8 microU/ml in control mice to 21 +/- 7 microU/ml (P less than .01). The peptide also inhibited the plasma insulin response to both glucose (P less than .01) and the cholinergic agonist carbachol (P less than .001). Furthermore, 2 min after injection of pancreastatin, plasma glucagon concentration had increased to 301 +/- 19 pg/ml compared to 190 +/- 12 pg/ml in control mice (P less than .001). The peptide did not, however, affect the carbachol-induced plasma glucagon response. In addition, pancreastatin induced a transient hyperglycemia. Combined adrenergic blockade by means of a pretreatment of phentolamine and propranolol did not prevent pancreastatin from exerting its effects on plasma insulin levels, whereas the increase in plasma glucagon levels was abolished. Thus, in the mouse, the newly discovered intrapancreatic peptide pancreastatin 1) lowers baseline plasma insulin levels, 2) inhibits glucose- and cholinergically induced insulin secretion, 3) stimulates baseline glucagon secretion, and 4) induces hyperglycemia.

Potentiation of glucose-induced insulin release by glucose in the isolated pancreas of fed and fasted rats.

Glucose, apart from its acute insulin-releasing effect, exerts a time-dependent potentiating action on subsequent stimulations of the pancreas. The influence of a 24-hour starvation on these two actions of glucose was studied with the completely isolated, perfused rat pancreas preparation. Starvation had no effect on the time kinetics of the insulin response, but the magnitudes of the early and late insulin-secretion phases were reduced to similar extents. It was demonstrated by using a wide glucose concentration range that the maximal insulin response is not significantly modified by starvation. In contrast, both the threshold of stimulation by and the Km for glucose were higher in the pancrease from fasted rats. Thus, starvation reduces the sensitivity of the islet for the insulin-releasing action of glucose. When the stimulatory concentrations of glucose were preceded for 40 minutes by the perfusion of 8.3 mM instead of the basal, 4.4 mM glucose, insulin secretion from the pancreas of fed animals was not modified. In contrast, raising the glucose concentration of the equilibrium period to 8.3 mM potentiated markedly the insulin response to subsequent stimulations in the pancreas from fasted rats. This potentiation expressed itself as increase in the maximal response: the Km for glucose was not reduced. Thus a 40-minute pretreatment with 8.3 mM glucose does not correct the diminished sensitivity induced by a 24-hour starvation. It is concluded that in starvation (1) the sensitivity for glucose of the mechanisms that initiate insulin release is diminished; (2) the sensitivity of the pancreas for the potentiation-inducing action of glucose is augumented. (3) In both respects, the insulin response of fasted rats is similar to that of mildly diabetic subjects. These and other findings suggest that the effect of glucose in initiation of insulin release and on generation of a state of potentiation in the islet are mediated by different mechanisms.

Normalization by insulin treatment of low mitochondrial glycerol phosphate dehydrogenase and pyruvate carboxylase in pancreatic islets of the GK rat.

The enzyme activity of the mitochondrial glycerol phosphate dehydrogenase (mGPD) in the pancreatic islet has been reported to be less than one-half of normal in the Goto-Kakizaki (GK) rat, a genetic model of NIDDM. In the current study, mGPD enzyme activity and the amount of mGPD protein, as judged by Western analysis, were 35-40% of normal in the islets of these animals. With the exception of pyruvate carboxylase, the activities of other enzymes were not abnormal. The assayable activity and amount of pyruvate carboxylase protein were decreased approximately 50% in the islets of the GK rats. Because mGPD, which is the key enzyme of the glycerol phosphate shuttle, and pyruvate carboxylase, which is the key component of the pyruvate malate shuttle, have been proposed to be essential for stimulus-secretion coupling in the pancreatic beta-cell, an important question is whether the decreases in these enzymes have a causal role in the hyperglycemia or whether the diabetic syndrome caused the decreases. To attempt to differentiate between these two possibilities, GK rats were treated with insulin to normalize their blood sugars. The activities of both mGPD and pyruvate carboxylase were also normalized by insulin treatment. An incidental discovery of this study was the identification of a high level of propionyl-CoA carboxylase activity and a lesser amount of methylcrotonyl-CoA carboxylase activity in pancreatic islets. These enzymes were normal in the islets of the GK rats. This is the first report on the presence of these two carboxylases in the islet and of low pyruvate carboxylase activity in the islet in NIDDM. We conclude that the decreased mGPD and pyruvate carboxylase in the pancreatic islet of the GK rat result from the diabetic syndrome.

Glucose tolerance, insulin release, and insulin sensitivity in normal-weight women with previous gestational diabetes mellitus.

Out of 57 women with previous histories of gestational diabetes (GD), 23 were of normal weight postpartum and willing to participate in three studies characterizing oral glucose tolerance (OGTT), insulin responsiveness to intravenous glucose (glucose infusion test, GIT), and insulin sensitivity (somatostatin, insulin, and glucose infusion test, SIGIT). The experiments were performed 6-36 mo after cessation of breast-feeding. The control group comprised 10 healthy women with normal OGTT matched for age and weight. Among subjects with previous histories of GD, 9 had normal, 8 borderline, and 6 decreased OGTT. As a group, women with previous histories of GD have significantly decreased insulin response and insulin sensitivity. Furthermore, all 14 with borderline and decreased OGTT demonstrated a low early insulin response during GIT (5-min value below the upper border of the lower quartile of normals), whereas insulin sensitivity was normal in 6 and low in 8 (glucose values attained during SIGIT were lower or higher, respectively, than the lower border of the upper quartile of controls). The women with previous histories of GD and normal OGTT exhibited normal (n = 4) and low (n = 5) insulin responses. Three of the former subjects had low and the remaining 6 had normal insulin sensitivity. In conclusion, as many as 60% of normal-weight women with previous histories of GD had borderline or decreased OGTT 6-36 mo postpartum. This derangement could be due to impaired early insulin response, which in some subjects was combined with low insulin sensitivity. Follow-up of women with previous histories of GD might enlighten the pathogenesis of non-insulin-dependent diabetes mellitus.

Basal and meal-induced somatostatin-like immunoreactivity in healthy subjects and in IDDM and totally pancreatectomized patients. Effects of acute blood glucose normalization.

We investigated the impact of blood glucose normalization on plasma levels of somatostatin-like immunoreactivity (SLI) in subjects with C-peptide-negative insulin-dependent diabetes mellitus (IDDM) and in totally pancreatectomized patients. Patients were studied during hyperglycemia and during normoglycemia, which was attained by Biostator-directed feedback insulin infusion. The experiments were performed in the fasted state and after a standardized breakfast. In IDDM (n = 6), basal levels of SLI were significantly higher than in nondiabetic subjects (n = 18). In IDDM, normalization of hyperglycemia was followed by a 40% decline in basal SLI (P less than .05). After the meal, SLI increased to the same absolute levels with or without feedback insulin treatment; however, the incremental response was 60% higher during feedback insulin treatment (P less than .05). Treatment also suppressed fasting and postprandial levels of glucagon, whereas gastric inhibitory polypeptide (GIP) levels were unaltered. In four pancreatectomized patients, normoglycemia tended to lower plasma levels of SLI by 50% (P less than .1). After breakfast, an SLI response was noted during normoglycemia, whereas no significant effect of the meal was seen during hyperglycemia. We conclude that in IDDM and in totally pancreatectomized patients, administration of insulin with subsequent normalization of blood glucose is accompanied by a decline in plasma levels of SLI in the fasted state, whereas the apparent response to a meal is enhanced. These effects on plasma levels of SLI probably reflect to a major extent release of somatostatin from the gastrointestinal tract.

Glibenclamide stimulates and glucose inhibits glucagon release induced by calcium deprivation.

The effects of low extracellular calcium levels on glibenclamide- and glucose-induced A-, B-, and D-cell secretion were investigated using the perfused pancreas preparation of the rat. At normal (2.6 mM) calcium, glucagon secretion was unaffected by glibenclamide (1 microgram/ml) and transiently suppressed by glucose (6.7 and 16.7 mM). Reduction of extracellular calcium to 0.24 mM promptly and persistently enhanced glucagon secretion in the presence of 3.3 mM glucose; this effect of low calcium was, however, diminished (P less than 0.001) by 54% and 61% when the glucose concentration was increased to 6.7 and 16.7 mM, respectively. In contrast, glibenclamide enhanced the glucagon response to calcium reduction, a twofold stimulation by the drug being observed at all glucose concentrations. Reduction of calcium to 0.24 mM failed to inhibit first-phase glibenclamide or glucose-induced insulin release; second phase was, however, inhibited whether induced by glibenclamide (in the presence of 6.7 mM glucose) or by glucose 16.7 mM per se. Reduction of calcium uniformly and completely abolished glibenclamide and glucose-induced somatostatin responses. It is concluded that: (1) the glucagon response induced by calcium deprivation is inhibited by glucose but potentiated by glibenclamide, and (2) reversal of a D-cell paracrine effect could underlie the glibenclamide effect.