Characterization of the portal signal in a nonsteady hyperglycemic state in conscious dogs

To characterize the "portal signal" in a nonsteady hyperglycemic state, the kinetic relationship between net hepatic glucose balance (NHGB) and either hepatic glucose load (HGL) or plasma insulin level was determined during glucose infusion using a catheter technique in 36 conscious dogs. Glucose was infused intraportally (Po group) and peripherally (Pe group) at 39, 56, and 83 micromol x kg(-1) x min(-1) over 2 h. There was a linear relationship between mean NHGB and either mean HGL or plasma insulin levels at each rate in either delivery (HGL: Po r = 0.99, Pe r = 0.95; insulin: Po r = 99, Pe r = 0.79). The threshold levels for net hepatic glucose uptake were 3.8 and 11.7 mmol/l for plasma glucose and 65 and 392 pmol/l for plasma insulin, respectively. The slope of the regression line against the abscissa was four times larger in portal than in peripheral delivery (HGL: Po 0.20 vs. Pe 0.05, P < 0.05; insulin: Po 0.19 vs. Pe 0.04, P < 0.05). These results suggest that the portal signal overrules the threshold of glucose for hepatic uptake by increasing hepatic extraction rate in a nonsteady hyperglycemic state.     

Effects of twinning, birth size, and postnatal growth on glucose tolerance and hypothalamic-pituitary-adrenal function in postpubertal sheep

Low birth weight is associated with postnatal physiological changes, including impaired glucose tolerance and increased cortisol secretion, that may predispose to disease in adulthood. Twins are born lighter than singletons, but there are conflicting data regarding the association between birth weight and postnatal physiology in twins. We studied glucose tolerance and ACTH and cortisol responses to a combined corticotropin-releasing hormone and arginine vasopressin (CRH + AVP) challenge in postpubertal female twin (n = 7 twin pairs) and singleton (n = 13) sheep from the same flock. There were no differences in glucose tolerance between twins and singletons and no association with birth weight. Twins had a greater ACTH (P < 0.05), but not cortisol, response to CRH + AVP than singletons. ACTH area under the curve was inversely related to birth weight in both singletons [R(2) = 0.31, P = 0.05; -8,311 (SD 3,736) pg.min.ml(-1).kg(-1)] and twins (R(2) = 0.49); in twins, this was due to the within-twin pair rather than the between-twin pair coefficient in the regression analysis [P = 0.02, -26,856 (9,806) vs. P = 0.1, 8,619 (4,950) pg.min.ml(-1).kg(-1)]. We conclude that the reduced fetal growth in twins has postnatal consequences for hypothalamic-pituitary-adrenal function and that this is determined by factors specific to the fetus (within-twin pair) rather than by shared maternal factors (between-twin pair). Studies investigating the associations between fetal growth and postnatal outcomes in twins benefit from an appropriate singleton control group and from analyses evaluating the contribution from both between- and within-pair coefficients in twins.     

Diminished glucagon suppression after β-cell reduction is due to impaired α-cell function rather than an expansion of α-cell mass

Impaired suppression of glucagon levels after oral glucose or meal ingestion is a hallmark of type 2 diabetes. Whether hyperglucagonemia after a β-cell loss results from a functional upregulation of glucagon secretion or an increase in α-cell mass is yet unclear. CD-1 mice were treated with streptozotocin (STZ) or saline. Pancreatic tissue was collected after 14, 21, and 28 days and examined for α- and β-cell mass and turnover. Intraperitoneal (ip) glucose tolerance tests were performed at day 28 as well as after 12 days of subcutaneous insulin treatment, and glucose, insulin, and glucagon levels were determined. STZ treatment led to fasting and post-challenge hyperglycemia (P < 0.001 vs. controls). Insulin levels increased after glucose injection in controls (P < 0.001) but were unchanged in STZ mice (P = 0.36). Intraperitoneal glucose elicited a 63.1 ± 4.1% glucagon suppression in control mice (P < 0.001), whereas the glucagon suppression was absent in STZ mice (P = 0.47). Insulin treatment failed to normalize glucagon levels. There was a significant inverse association between insulin and glucagon levels after ip glucose ingestion (r(2) = 0.99). β-Cell mass was reduced by ～75% in STZ mice compared with controls (P < 0.001), whereas α-cell mass remained unchanged (P > 0.05). α-Cell apoptosis (TUNEL) and replication (Ki67) were rather infrequently noticed, with no significant differences between the groups. These studies underline the importance of endogenous insulin for the glucose-induced suppression of glucagon secretion and suggest that the insufficient decline in glucagon levels after glucose administration in diabetes is primarily due to a functional loss of intraislet inhibition of α-cell function rather than an expansion of α-cell mass.     

Identification of a novel GPR119 agonist, AS1269574, with in vitro and in vivo glucose-stimulated insulin secretion

The G protein-coupled receptor 119 (GPR119) is highly expressed in pancreatic β-cells. On activation, this receptor enhances the effect of glucose-stimulated insulin secretion (GSIS) via the elevation of intracellular cAMP concentrations. Although GPR119 agonists represent promising oral antidiabetic agents for the treatment of type 2 diabetes therapy, they suffer from the inability to adequately directly preserve β-cell function. To identify a new structural class of small-molecule GPR119 agonists with both GSIS and the potential to preserve β-cell function, we screened a library of synthetic compounds and identified a candidate molecule, AS1269574, with a 2,4,6-tri-substituted pyrimidine core. Here, we examined the preliminary in vitro and in vivo effects of AS1269574 on insulin secretion and glucose tolerance. AS1269574 had an EC₅₀ value of 2.5 μM in HEK293 cells transiently expressing human GPR119 and enhanced insulin secretion in the mouse pancreatic β-cell line MIN-6 only under high-glucose (16.8 mM) conditions. This contrasted with the action of the sulfonylurea glibenclamide, which also induced insulin secretion under low-glucose conditions (2.8 mM). In in vivo studies, a single administration of AS1269574 to normal mice reduced blood glucose levels after oral glucose loading based on the observed insulin secretion profiles. Significantly, AS1269574 did not affect fed and fasting plasma glucose levels in normal mice. Taken together, these results suggest that AS1269574 represents a novel structural class of small molecule, orally administrable GPR119 agonists with GSIS and promising potential for the treatment of type 2 diabetes.     

Inhibition of the receptor for advanced glycation endproducts (RAGE) protects pancreatic β-cells

Advanced glycation endproducts (AGEs) and the receptor for AGEs (RAGE) have been linked to the pathogenesis of diabetic complications, such as retinopathy, neuropathy, and nephropathy. AGEs may induce β-cell dysfunction and apoptosis, another complication of diabetes. However, the role of AGE-RAGE interaction in AGE-induced pancreatic β-cell failure has not been fully elucidated. In this study, we investigated whether AGE–RAGE interaction could mediate β-cell failure. We explored the potential mechanisms in insulin secreting (INS-1) cells from a pancreatic β-cell line, as well as primary rat islets. We found that glycated serum (GS) induced apoptosis in pancreatic β-cells in a dose- and time-dependent manner. Treatment with GS increased RAGE protein production in cultured INS-1 cells. GS treatment also decreased bcl-2 gene expression, followed by mitochondrial swelling, increased cytochrome c release, and caspase activation. RAGE antibody and knockdown of RAGE reversed the β-cell apoptosis and bcl-2 expression. Inhibition of RAGE prevented AGE-induced pancreatic β-cell apoptosis, but could not restore the function of glucose stimulated insulin secretion (GSIS) in rat islets. In summary, the results of the present study demonstrate that AGEs are integrally involved in RAGE-mediated apoptosis and impaired GSIS dysfunction in pancreatic β-cells. Inhibition of RAGE can effectively protect β-cells against AGE-induced apoptosis, but cannot reverse islet dysfunction in GSIS.     

Maternal and fetal growth, body composition, endocrinology, and metabolic status in undernourished adolescent sheep

The influence of relative maternal undernutrition on growth, endocrinology, and metabolic status in the adolescent ewe and her fetus were investigated at Days 90 and 130 of gestation. Singleton pregnancies to a single sire were established, and thereafter ewes were offered an optimal control (C; n = 14) or low (L [0.7 x C]; n = 21) dietary intake. Seven ewes receiving the L intake were switched to the C intake on Day 90 of gestation (L-C). At Day 90, live weight and adiposity score were reduced (P < 0.001) in L versus C dams. Plasma insulin and IGF1 concentrations were decreased (P < 0.02), whereas glucose concentrations were preserved in L relative to C intake dams. Fetal and placental mass was independent of maternal nutrition at this stage. By Day 130 of gestation, when compared to C and L-C dams, maternal adiposity was further depleted in L intake dams; concentrations of insulin, IGF1, and glucose were reduced; and nonesterified fatty acids increased. At Day 130, placental mass remained independent of maternal nutrition, but body weight was reduced (P < 0.01) in L compared with C fetuses (3555 g vs. 4273 g). Body weight was intermediate (3836 g) in L-C fetuses. Plasma glucose (P < 0.03), insulin (P < 0.07), and total liver glycogen content (P < 0.04) were attenuated in L fetuses. Fetal carcass analyses revealed absolute reductions (P < 0.05) in dry matter, crude protein, and fat, and a relative (g/kg) increase in carcass ash (P < 0.01) in L compared with C fetuses. Thus, limiting maternal intake during adolescent pregnancy gradually depleted maternal body reserves, impaired fetal nutrient supply, and slowed fetal soft tissue growth.     

AS1907417, a novel GPR119 agonist, as an insulinotropic and β-cell preservative agent for the treatment of type 2 diabetes

G-protein-coupled receptor (GPR) 119 is involved in glucose-stimulated insulin secretion (GSIS) and represents a promising target for the treatment of type 2 diabetes as it is highly expressed in pancreatic β-cells. Although a number of oral GPR119 agonists have been developed, their inability to adequately directly preserve β-cell function limits their effectiveness. Here, we evaluated the therapeutic potential of a novel small-molecule GPR119 agonist, AS1907417, which represents a modified form of a 2,4,6-tri-substituted pyrimidine core agonist, AS1269574, we previously identified. The exposure of HEK293 cells expressing human GPR119, NIT-1 cells expressing human insulin promoter, and the pancreatic β-cell line MIN-6-B1 to AS1907417, enhanced intracellular cAMP, GSIS, and human insulin promoter activity, respectively. In in vivo experiments involving fasted normal mice, a single dose of AS1907417 improved glucose tolerance, but did not affect plasma glucose or insulin levels. Twice-daily doses of AS1907417 for 4 weeks in diabetic db/db, aged db/db mice, ob/ob mice, and Zucker diabetic fatty rats reduced hemoglobin A1c levels by 1.6%, 0.8%, 1.5%, and 0.9%, respectively. In db/db mice, AS1907417 improved plasma glucose, plasma insulin, pancreatic insulin content, lipid profiles, and increased pancreatic insulin and pancreatic and duodenal homeobox 1 (PDX-1) mRNA levels. These data demonstrate that novel GPR119 agonist AS1907417 not only effectively controls glucose levels, but also preserves pancreatic β-cell function. We therefore propose that AS1907417 represents a new type of antihyperglycemic agent with promising potential for the effective treatment of type 2 diabetes.     

The CB1 Antagonist Rimonabant Decreases Insulin Hypersecretion in Rat Pancreatic Islets

Type 2 diabetes and obesity are characterized by elevated nocturnal circulating free fatty acids, elevated basal insulin secretion, and blunted glucose‐stimulated insulin secretion (GSIS). The CB1 receptor antagonist, Rimonabant, has been shown to improve glucose tolerance and insulin sensitivity in vivo but its direct effect on islets has been unclear. Islets from lean littermates and obese Zucker (ZF) and Zucker Diabetic Fatty (ZDF) rats were incubated for 24 h in vitro and exposed to 11 mmol/l glucose and 0.3 mmol/l palmitate (GL) with or without Rimonabant. Insulin secretion was determined at basal (3 mmol/l) or stimulatory (15 mmol/l) glucose concentrations. As expected, basal secretion was significantly elevated in islets from obese or GL‐treated lean rats whereas the fold increase in GSIS was diminished. Rimonabant decreased basal hypersecretion in islets from obese rats and GL‐treated lean rats without decreasing the fold increase in GSIS. However, it decreased GSIS in islets from lean rats without affecting basal secretion. These findings indicate that Rimonabant has direct effects on islets to reduce insulin secretion when secretion is elevated above normal levels by diet or in obesity. In contrast, it appears to decrease stimulated secretion in islets from lean animals but not in obese or GL‐exposed islets.     

Emergence of insulin resistance in juvenile baboon offspring of mothers exposed to moderate maternal nutrient reduction

Developmental programming of postnatal pancreatic β-cell and peripheral insulin function by maternal nutrient reduction (MNR) has been extensively investigated in rodents and sheep, but no data exist from nonhuman primate offspring of MNR mothers. We hypothesized that moderate levels of MNR would result in developmental programming of postnatal β-cell function and peripheral insulin sensitivity that lead to emergence of a prediabetic state prior to puberty. Prepregnancy phenotype of 18 nonpregnant baboons was matched. During pregnancy and lactation 12 mothers ate chow ad libitum (controls), while six ate 70% of chow consumed by controls (weight-adjusted MNR). Weaned offspring ate normal chow. At 3.5 ± 0.18 yr (mean ± SE) in an intravenous glucose tolerance test, conscious, tethered MNR juvenile offspring (2 females and 4 males) showed increased fasting glucose (P < 0.04), fasting insulin (P < 0.04), and insulin area under the curve (AUC; P < 0.01) compared with controls (8 females and 4 males). Insulin AUC also increased following an arginine challenge (P < 0.02). Baseline homeostatic model assessment insulin β-cell sensitivity was greater in MNR offspring than controls (P < 0.03). In a hyperinsulinemic, euglycemic clamp, the glucose disposal rate decreased 26% in MNR offspring. Changes observed were not sex dependent. MNR in pregnancy and lactation programs offspring metabolic responses, increasing insulin resistance and β-cell responsiveness, resulting in emergence of an overall phenotype that would predispose to later life type-2 diabetes, especially, should other dietary challenges such as a Westernized diet be experienced.     

Cell cycle control of β-cell replication in the prenatal and postnatal human pancreas

β-Cell regeneration declines with aging, but the molecular mechanisms controlling β-cell replication in humans are not well understood. We compared the expression of selected cell cycle proteins in prenatal and adult tissue and examined the association of these proteins with β-cell replication. Pancreatic tissue from a total of 20 human fetuses and adults was stained for Ki67, cyclin D3, p16 and p27, and insulin. The β-cellular expression of these cell cycle proteins was determined. The frequency of β-cell replication was lower in adult compared with prenatal β-cells (<0.5 vs. 3.4 ± 0.5%, respectively; P < 0.0001). p16 was sporadically expressed in prenatal β-cells (8.0 ± 1.1%) but highly enriched in adult β-cells (63.1 ± 5.2%, P < 0.0001). Likewise, the expression of p27 was much lower in prenatal β-cells (1.7 ± 0.4 vs. 44.1 ± 5.4%, respectively, P < 0.0001), and cyclin D3 expression increased from 24.2 ± 4.1 to 47.25 ± 5.0%, respectively (P < 0.001), with aging. The expression of all three proteins was significantly correlated with each other (P < 0.01 and r > 0.75, respectively). The strong expression of cyclin D3 in adult human β-cells and its correlation to p27 and p16 suggest a positive role in human β-cell cycle regulation. p16 and p27 appear to restrict β-cell replication with aging. The age dependency of cell cycle regulation in human β-cells might explain the reduced β-cell regeneration in adult humans.     

Changes to metabolite concentration in fetal sheep subjected to prolonged hypobaric hypoxia

The effect of hypobaric hypoxaemia on the concentration of metabolic substrates in the ovine fetus and pregnant ewe with implanted vascular catheters, was investigated. At 120 to 141 days of gestation sheep were subjected to hypobaria (mean fetal carotid PO2 12.7 +/- 0.7 torr; n = 9) or normobaria (mean fetal carotid PO2 22.7 +/- 0.7 torr; n = 11; P less than 0.001). At 141 days gestation mean fetal weight was 3.46 +/- 0.72 kg in the hypobaric group compared to 4.15 +/- 0.51 in the normobaric group (P less than 0.05). Concentrations of glucose in maternal and fetal plasma and fructose in fetal plasma were similar in hypobaric and normobaric fetuses. The concentration of lactate in fetal plasma rose from 1.68 +/- 1.34 to 8.79 +/- 5.8 mmol/l (P less than 0.001) within 24 h of onset of hypoxia, but fell to 3.36 +/- 1.13 mmol/l by day 3 of treatment, though still significantly above the concentration of lactate in the control fetuses (1.47 +/- 0.47; P less than 0.001). There was no significant effect of hypoxia on the concentration of lactate or alanine in maternal plasma. Alanine concentration in the plasma of fetuses subjected to hypoxia significantly increased within 24 h of exposure (0.28 +/- 0.10 vs 0.58 +/- 0.39 mmol/l; P less than 0.01) and remained elevated for the duration of the study. There was no significant effect of gestational age on the concentration of metabolic substrates in either the control or experimental groups. Hypoxia is associated with a sustained rise in the concentration of plasma lactate and alanine in the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Programming of glucose-insulin metabolism in adult sheep after maternal undernutrition

The present study examines the effects of late vs. early gestation undernutrition on adult glucose-insulin homeostasis in sheep and investigates whether the lower birth weight of twins alters glucose-insulin handling in adult life. Pregnant sheep were fed to requirement (100% intake) from day 0 of gestation to term [ approximately 147 days of gestation (dGA), control singles (CS) n = 5; control twins (CT) n = 5] or to 50% requirement from days 0-30 dGA [nutrient restricted during early gestation (NRE); n = 5] or day 110-term [NR during late nutrition (NRL); n = 4]. At all other times, NR sheep received 100% intake. All sheep lambed naturally; offspring were weaned at 10 wk and were reared on pasture until 1 yr of age. At this time, indwelling catheters were inserted, and 2-4 days later, basal metabolic and endocrine status and responses to an intravenous glucose tolerance test (IVGTT) and feeding were assessed. Adipose and skeletal muscle were then sampled after humane euthanasia and were analyzed for expression of insulin-signaling proteins and GLUT4. Between groups, birth weight of singletons was similar and increased relative to twins. At 1 yr of age, weights were similar between groups. The areas under the curve for glucose and insulin during the IVGTT were greater in NRL vs. other groups, indicating glucose intolerance. This was associated with reduced adipose, but not muscle, GLUT4, and increased adipose tissue mass. Adult glucose-insulin homeostasis in sheep was unaffected by fetal number. In conclusion, prenatal undernutrition, specifically during late gestation, affects adult offspring intermediary metabolism, and, in particular, glucose-insulin homeostasis.     

D-Glyceraldehyde causes production of intracellular peroxide in pancreatic islets, oxidative stress, and defective beta cell function via non-mitochondrial pathways

D-Glyceraldehyde (D-GLYC) is usually considered to be a stimulator of insulin secretion but theoretically can also form reactive oxygen species (ROS), which can inhibit beta cell function. We examined the time- and concentration-dependent effects of D-GLYC on insulin secretion, insulin content, and formation of ROS. We observed that a 2-h exposure to 0.05-2 mM D-GLYC potentiated glucose-stimulated insulin secretion (GSIS) in isolated Wistar rat islets but that higher concentrations inhibited GSIS. A 24-h exposure to 2 mm D-GLYC inhibited GSIS, decreased insulin content, and increased intracellular peroxide levels (2.14 +/- 0.31-fold increase, n = 4, p < 0.05). N-Acetylcysteine (10 mM) prevented the increase in intracellular peroxides and the adverse effects of d-GLYC on GSIS. In the presence of 11.1 but not 3.0 mm glucose, koningic acid (10 microM), a specific glyceraldehyde-3-phosphate dehydrogenase inhibitor, increased intracellular peroxide levels (1.88 +/- 0.30-fold increase, n = 9, p < 0.01) and inhibited GSIS (control GSIS = p < 0.001; koningic acid GSIS, not significant). To determine whether oxidative phosphorylation was the source of ROS formation, we cultured rat islets with mitochondrial inhibitors. Neither rotenone or myxothiazol prevented D-GLYC-induced increases in islet ROS. Adenoviral overexpression of manganese superoxide dismutase also failed to prevent the effect of D-GLYC to increase ROS levels. These observations indicate that exposure to excess D-GLYC increases reactive oxygen species in the islet via non-mitochondrial pathways and suggest the hypothesis that the oxidative stress associated with elevated D-GLYC levels could be a mechanism for glucose toxicity in beta cells exposed chronically to high glucose concentrations.     

Circulating leptin concentrations are positively related to leptin messenger RNA expression in the adipose tissue of fetal sheep in the pregnant ewe fed at or below maintenance energy requirements during late gestation

We have investigated the effects of maternal undernutrition during late gestation on maternal and fetal plasma concentrations of leptin and on leptin gene expression in fetal perirenal adipose tissue. Pregnant ewes were randomly assigned at 115 days of gestation (term = 147 +/- 3 days [mean +/- SEM]) to either a control group (n = 13) or an undernourished group (n = 16) that received approximately 50% of the control diet until 144-147 days of gestation. Maternal plasma glucose, but not leptin, concentrations were lower in the undernourished ewes. A significant correlation was found, however, between mean maternal plasma leptin (y) and glucose (x) concentrations (y = 2.9x - 2.4; r = 0.51, P < 0.02) when the control and undernourished groups were combined. Fetal plasma glucose and insulin, but not fetal leptin, concentrations were lower in the undernourished ewes, and no correlation was found between mean fetal leptin concentrations and either mean fetal glucose or insulin concentrations. A positive relationship, however, was found between mean fetal (y) and maternal (x) plasma leptin concentrations (y = 0.18x + 0.45; r = 0.66, P < 0.003). No significant difference was found in the relative abundance of leptin mRNA in fetal perirenal fat between the undernourished (0.60 +/- 0.09, n = 10) and control (0.70 +/- 0.08, n = 10) groups. Fetal plasma concentrations of leptin (y) and leptin mRNA levels (x) in perirenal adipose tissue were significantly correlated (y = 1.5x +/- 0.3; r = 0.69, P < 0.05). In summary, the capacity of leptin to act as a signal of moderate maternal undernutrition may be limited before birth in the sheep.     

Moderate effect of duodenal-jejunal bypass surgery on glucose homeostasis in patients with type 2 diabetes

Gastric bypass surgery causes resolution of type 2 diabetes (T2DM), which has led to the hypothesis that upper gastrointestinal (UGI) tract diversion, itself, improves glycemic control. The purpose of this study was to determine whether UGI tract bypass without gastric exclusion has therapeutic effects in patients with T2DM. We performed a prospective trial to assess glucose and β-cell response to an oral glucose load before and at 6, 9, and 12 months after duodenal-jejunal bypass (DJB) surgery. Thirty-five overweight or obese adults (BMI: 27.0 ± 4.0 kg/m(2)) with T2DM and 35 sex-, age-, race-, and BMI-matched subjects with normal glucose tolerance (NGT) were studied. Subjects lost weight after surgery, which was greatest at 3 months (6.9 ± 4.9%) with subsequent regain to 4.2 ± 5.3% weight loss at 12 months after surgery. Glycated hemoglobin (HbA(1c)) decreased from 9.3 ± 1.6% before to 7.7 ± 2.0% at 12 months after surgery (P < 0.001), in conjunction with a 20% decrease in the use of diabetes medications (P < 0.05); 7 (20%) subjects achieved remission of diabetes (no medications and HbA(1c) <6.5%). The area under the curve after glucose ingestion was ~20% lower for glucose but doubled for insulin and C-peptide at 12 months, compared with pre-surgery values (all P < 0.01). However, the β-cell response was still 70% lower than subjects with NGT (P < 0.001). DJB surgery improves glycemic control and increases, but does not normalize the β-cell response to glucose ingestion. These findings suggest that altering the intestinal site of delivery of ingested nutrients has moderate therapeutic effects by improving β-cell function and glycemic control.     

Effects of S-nitroso-N-acetyl-penicillamine administration on glucose tolerance and plasma levels of insulin and glucagon in the dog.

It has been suggested that nitric oxide (NO, nitrogen monoxide) is a regulator of carbohydrate metabolism in skeletal muscle. The present study was undertaken to investigate the acute effects of the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) on blood glucose levels and on the gluco-regulatory hormones insulin and glucagon in healthy dogs. The acute effects of SNAP on mean arterial pressure and heart rate were also investigated. The drug was administered intravenously and the pre- and postprandial blood glucose, plasma insulin, and glucagon concentrations were determined at half-hour time intervals postadministration after a glucose challenge. The plasma nitrate and nitrite concentrations were measured and taken as the biochemical markers of in vivo NO formation. The oral glucose tolerance test revealed an impaired glucose tolerance in SNAP-treated dogs as reflected by the area under the glucose curve, 1150.50 +/- 63.00 mmol x 150 min and 1355.25 +/- 102.01 mmol/L x 150 min in dogs treated with 10 and 20 mg/kg of SNAP, respectively, compared with 860.25 +/- 60.68 mmol/L x 150 min in captopril-treated controls (P < 0.05). The 2-h blood glucose concentration in dogs treated with 20 mg/kg body wt of SNAP was 9.17 +/- 1.10 mmol/L compared with 5.59 +/- 0.26 mmol/L for captopril-treated controls (P = 0.015). The oral glucose tolerance test also confirmed an impaired insulin secretion in the SNAP-treated dogs. While the plasma insulin concentration increased gradually in the captopril-treated controls to a peak value of 39.50 +/- 2.55 microIU/ml, 1.5 h after a glucose challenge there was a decrease in the plasma insulin concentration in SNAP-treated dogs to a low value of 20.67 +/- 0.88 microIU/ml (P = 0.006). In contrast, there were no significant differences in plasma glucagon concentration in SNAP-treated dogs and captopril-treated dogs at any time points. Using the Griess reaction, we found that there was a 27-95% increase in plasma nitrate/nitrite concentration on administration of SNAP. The sustained hyperglycemic effect observed in SNAP-treated dogs was accompanied by a marginal decrease in the mean arterial blood pressure and a significant increase in heart rate (P < 0.05). We conclude that acute administration of SNAP in the oral glucose tolerance test releases NO that modulates the parameters of carbohydrate metabolism.     

Prolonged infusion of amino acids increases leucine oxidation in fetal sheep

Maternal high-protein supplements designed to increase birth weight have not been successful. We recently showed that maternal amino acid infusion into pregnant sheep resulted in competitive inhibition of amino acid transport across the placenta and did not increase fetal protein accretion rates. To bypass placental transport, singleton fetal sheep were intravenously infused with an amino acid mixture (AA, n = 8) or saline [control (Con), n = 10] for ～12 days during late gestation. Fetal leucine oxidation rate increased in the AA group (3.1 ± 0.5 vs. 1.4 ± 0.6 μmol·min(-1)·kg(-1), P < 0.05). Fetal protein accretion (2.6 ± 0.5 and 2.2 ± 0.6 μmol·min(-1)·kg(-1) in AA and Con, respectively), synthesis (6.2 ± 0.8 and 7.0 ± 0.9 μmol·min(-1)·kg(-1) in AA and Con, respectively), and degradation (3.6 ± 0.6 and 4.5 ± 1.0 μmol·min(-1)·kg(-1) in AA and Con, respectively) rates were similar between groups. Net fetal glucose uptake decreased in the AA group (2.8 ± 0.4 vs. 3.9 ± 0.1 mg·kg(-1)·min(-1), P < 0.05). The glucose-O(2) quotient also decreased over time in the AA group (P < 0.05). Fetal insulin and IGF-I concentrations did not change. Fetal glucagon increased in the AA group (119 ± 24 vs. 59 ± 9 pg/ml, P < 0.05), and norepinephrine (NE) also tended to increase in the AA group (785 ± 181 vs. 419 ± 76 pg/ml, P = 0.06). Net fetal glucose uptake rates were inversely proportional to fetal glucagon (r(2) = 0.38, P < 0.05), cortisol (r(2) = 0.31, P < 0.05), and NE (r(2) = 0.59, P < 0.05) concentrations. Expressions of components in the mammalian target of rapamycin signaling pathway in fetal skeletal muscle were similar between groups. In summary, prolonged infusion of amino acids directly into normally growing fetal sheep increased leucine oxidation. Amino acid-stimulated increases in fetal glucagon, cortisol, and NE may contribute to a shift in substrate oxidation by the fetus from glucose to amino acids.     

High normal HbA(1c) levels were associated with impaired insulin secretion without escalating insulin resistance in Japanese individuals: the Toranomon Hospital Health Management Center Study 8 (TOPICS 8)

Diabet. Med. 29, 1285-1290 (2012) ABSTRACT: Aims We aimed to characterize the association of insulin resistance, impaired insulin secretion and β-cell dysfunction in relation to HbA(1c) levels in a non-diabetic range in Japanese individuals without clinically diagnosed diabetes. Methods This cross-sectional study included 1444 individuals without a history of outpatient treatment of diabetes or use of insulin or oral hypoglycaemic agents. The homeostasis model assessment of insulin resistance and beta-cell function, insulinogenic index, Matsuda index and disposition index were calculated using data from 75-g oral glucose tolerance tests and compared across quintile (Q) categories of HbA(1c) levels. Results Fasting plasma glucose and 30-min and 60-min plasma glucose (PG) levels were significantly higher when HbA(1c) exceeded 36?mmol/mol (5.4%). A HbA(1c) concentration of 36-37?mmol/mol (5.4-5.5%) (Q3) was significantly associated with a 15% lower homeostasis model assessment of β-cell function value and 31% lower insulinogenic index value compared with HbA(1c) ≤?32?mmol/mol (≤?5.1%) (Q1) (P?<0.01). Further, a HbA(1c) concentration of 38-40?mmol/mol (5.6-5.8%) (Q4) was associated with 17% (P?<0.01) and 24% (P?<0.05) reductions in those indexes, respectively. However, the homeostasis model assessment of insulin resistance was not significantly elevated and the Matsuda index was not significantly lower unless HbA(1c) exceeded 41?mmol/mol (5.9%). Individuals with HbA(1c) ≥?41?mmol/mol (≥?5.9%) (Q5) had a 69% lower disposition index than those with a HbA(1c) concentration of ≤?32?mmol/mol (≤?5.1%) (Q1). Conclusions Elevated HbA(1c) levels ≥?41?mmol/mol (≥?5.9%) were associated with substantial reductions in insulin secretion, insulin sensitivity and β-cell dysfunction in Japanese individuals not treated for diabetes. High normal HbA(1c) levels of 36-40?mmol/mol (5.4-5.8%) were also associated with impaired insulin secretion without marked insulin resistance in Japanese individuals.     

Taurine supplementation prevents morpho-physiological alterations in high-fat diet mice pancreatic β-cells

Taurine (Tau) is involved in beta (β)-cell function and insulin action regulation. Here, we verified the possible preventive effect of Tau in high-fat diet (HFD)-induced obesity and glucose intolerance and in the disruption of pancreatic β-cell morpho-physiology. Weaning Swiss mice were distributed into four groups: mice fed on HFD diet (36 % of saturated fat, HFD group); HTAU, mice fed on HFD diet and supplemented with 5 % Tau; control (CTL); and CTAU. After 19 weeks of diet and Tau treatments, glucose tolerance, insulin sensitivity and islet morpho-physiology were evaluated. HFD mice presented higher body weight and fat depots, and were hyperglycemic, hyperinsulinemic, glucose intolerant and insulin resistant. Their pancreatic islets secreted high levels of insulin in the presence of increasing glucose concentrations and 30 mM K⁺. Tau supplementation improved glucose tolerance and insulin sensitivity with a higher ratio of Akt phosphorylated (pAkt) related to Akt total protein content (pAkt/Akt) following insulin administration in the liver without altering body weight and fat deposition in HTAU mice. Isolated islets from HTAU mice released insulin similarly to CTL islets. HFD intake induced islet hypertrophy, increased β-cell/islet area and islet and β-cell mass content in the pancreas. Tau prevented islet and β-cell/islet area, and islet and β-cell mass alterations induced by HFD. The total insulin content in HFD islets was higher than that of CTL islets, and was not altered in HTAU islets. In conclusion, for the first time, we showed that Tau enhances liver Akt activation and prevents β-cell compensatory morpho-functional adaptations induced by HFD.     

Potentiation of the early-phase insulin response by a prior meal contributes to the second-meal phenomenon in type 2 diabetes

Improved glucose tolerance following a sequential meal is known as the second-meal phenomenon. We aimed to investigate its extent and underlying mechanisms in patients with type 2 diabetes. Metabolic responses after lunch in 12 diabetic patients were compared on two separate days: one with (Day BL) and another without (Day FL) breakfast. The responses of hormones were calculated by the incremental area under the curve (iAUC) values for 180 min after each meal. Indexes of early-phase insulin secretion were assessed, and β-cell function was estimated by mathematical modeling. [iAUC(glucose(180-360 min))] was significantly lower on Day BL than on Day FL (181 ± 43 vs. 472 ± 29 mmol·liter(-1)·min, P = 0.0005). The magnitude of the The second-meal phenomenon [iAUC(glucose(180-360 min)) on Day BL/Day FL] was 35 ± 9%. The peak levels of insulin and C-peptide were attained 45 min earlier after the second meal than after the first meal. iAUC(glucose(180-360 min)) correlated negatively with iAUC(insulin(180-210 min)) (r = -0.443, P = 0.0300), insulinogenic index (r = -0.769, P < 0.0001), acute C-peptide response (r = -0.596, P = 0.0021), and potentiation factor [i.e., potentiation effect on insulin secretion] ratio (180-360)/(0-20) (r = -0.559, P = 0.0045), while correlated positively with free fatty acid level before lunch (r = 0.679, P = 0.0003). The second-meal phenomenon was evident in patients with type 2 diabetes. Potentiation of the early-phase insulin response by a prior meal contributes to this phenomenon in type 2 diabetes.