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Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) regulate islet function after carbohydrate ingestion. Whether incretin hormones are of importance for islet function after ingestion of noncarbohydrate macronutrients is not known. This study therefore examined integrated incretin and islet hormone responses to ingestion of pure fat (oleic acid; 0.88 g/kg) or protein (milk and egg protein; 2 g/kg) over 5 h in healthy men, aged 20-25 yr (n = 12); plain water ingestion served as control. Both intact (active) and total GLP-1 and GIP levels were determined as was plasma activity of dipeptidyl peptidase-4 (DPP-4). Following water ingestion, glucose, insulin, glucagon, GLP-1, and GIP levels and DPP-4 activity were stable during the 5-h study period. Both fat and protein ingestion increased insulin, glucagon, GIP, and GLP-1 levels without affecting glucose levels or DPP-4 activity. The GLP-1 responses were similar after protein and fat, whereas the early (30 min) GIP response was higher after protein than after fat ingestion (P < 0.001). This was associated with sevenfold higher insulin and glucagon responses compared with fat ingestion (both P < 0.001). After protein, the early GIP, but not GLP-1, responses correlated to insulin ([r.sup.2] = 0.86; P = 0.0001) but not glucagon responses. In contrast, after fat ingestion, GLP-I and GIP did not correlate to islet hormones. We conclude that, whereas protein and fat release both incretin and islet hormones, the early GIP secretion after protein ingestion may be of primary importance to islet hormone secretion. insulin; glucagon; glucagon-like peptide-1; glucose-dependent insulinotropic polypeptide; incretins; man

Neural and endocrine factors (i.e., Ach and GLP-1) restore defective glucose-stimulated insulin release in pancreatic islets lacking sulfonylurea type 1 receptors (SUR[1.sup.-/-]) (Doliba NM, Qin W, Vatamaniuk MZ, Li C, Zelent D, Najafi H, Buettger CW, Collins HW, Carr RD, Magnuson MA, and Matschinsky FM. Am J Physiol Endocrinol Metab 286: E834-E843, 2004). The goal of the present study was to assess fuel-induced respiration in SUR[1.sup.-/-] islets and to correlate it with changes in intracellular [Ca.sup.2+], insulin, and glucagon secretion. By use of a method based on [O.sub.2] quenching of phosphorescence, the [O.sub.2] consumption rate (OCR) of isolated islets was measured online in a perifusion system. Basal insulin release (IR) was 7-10 times higher in SUR[1.sup.-/-] compared with control (CON) islets, but the OCR was comparable. The effect of high glucose (16.7 mM) on IR and OCR was markedly reduced in SUR[1.supp.-/-] islets compared with CON. Ach (0.5 [micro]M) in the presence of 16.7 mM glucose caused a large burst of IR in CON and SUR[1.supp.-/-] islets with minor changes in OCR in both groups of islets. In SUR[1.supp.-/-] islets, high glucose failed to inhibit glucagon secretion during stimulation with amino acids or Ach. We conclude that 1) reduced glucose responsiveness of SUR[1.sup.-/-] islets may be in part due to impaired energetics, as evidenced by significant decrease in glucose-stimulated OCR; 2) elevated intracellular [Ca.sup.2+] levels may contribute to altered insulin and glucagon secretion in SUR[1.sup.-/-] islets; and 3) The amplitudes of the changes in OCR during glucose and Ach stimulation do not correlate with IR in normal and SUR[1.sup.-/-] islets suggesting that the energy requirements for exocytosis are minor compared with other ATP-consuming reactions. sulfonylurea receptor 1 knockout mice; acetylcholine; insulin and glucagon release; calcium; oxygen consumption doi: 10.1152/ajpendo.00579.2005

At present, the best available estimators of [beta]-cell mass in humans are those based on measurement of insulin levels or appearance rates in the circulation. In several animal models, these estimators have been validated against [beta]-cell mass in lean animals. However, as many diabetic humans are obese, a correlation between in vivo tests and [beta]-cell mass must be evaluated over a range of body weights to include different levels of insulin sensitivity. For this purpose, obese (n = 10) and lean (n = 25) Gottingen minipigs were studied. [beta]-Cell mass had been reduced (n = 16 lean, n = 5 obese) with a combination of nicotinamide (67 mg/kg) and streptozotocin (125 mg/kg), acute insulin response (AIR) to intravenous glucose and/or arginine was tested, pulsatile insulin secretion was evaluated by deconvolution (n = 30), and [beta]-cell mass was determined histologically. AIR to 0.3 ([r.sup.2] = 0.4502, P < 0.0001) or 0.6 g/kg glucose ([r.sup.2] = 0.6806, P < 0.0001), 67 mg/kg arginine ([r.sup.2] = 0.5730, P < 0.001), and maximum insulin concentration ([r.sup.2] = 0.7726, P < 0.0001) were all correlated to [beta]-cell mass when evaluated across study groups, and regression lines were not different between lean and obese groups except for AIR to 0.3 g/kg glucose. Baseline pulse mass was not significantly correlated to [beta]-cell mass across the study groups ([r.sup.2] = 0.1036, NS), whereas entrained pulse mass did show a correlation across groups ([r.sup.2] = 0.4049, P < 0.001). This study supports the use of in vivo tests of insulin responses to evaluate [beta]-cell mass over a range of body weights in the minipig. Extensive stimulation of insulin secretion by a combination of glucose and arginine seems to give the best correlation to [beta]-cell mass. animal model; streptozotocin; arginine; pulsatile insulin secretion

We investigated the effect of subdiaphragmatic vagal deafferentation (SDA) on food intake, body weight gain, and metabolism in obese (fa/fa) and lean (Fa/?) Zucker rats. Before and after recovery from surgery, food intake and body weight gain were recorded, and plasma glucose and insulin were measured in tail-prick blood samples. After implantation of a jugular vein catheter, an intravenous glucose tolerance test (IVGTT) was performed, followed by minimal modeling to estimate the insulin sensitivity index. Food intake relative to metabolic body weight (g/[kg.sup.0.75]) and daily body weight gain after surgery were lower (P < 0.05) in SDA than in sham obese but not lean rats. Before surgery, plasma glucose and insulin concentrations were lower (P < 0.05) in lean than in obese rats but did not differ between surgical groups within both genotypes. Four weeks after surgery, plasma glucose and insulin were still similar in SDA and sham lean rats but lower (P < 0.05) in SDA than in sham obese rats. IVGTT revealed a downward shift of the plasma insulin profile by SDA in obese but not lean rats, whereas the plasma glucose profile was unaffected. SDA decreased (P < 0.05) area under the curve for insulin but not glucose in obese rats. The insulin sensitivity index was higher in lean than in obese rats but was not affected by SDA in both genotypes. These results suggest that elimination of vagal afferent signals from the upper gut reduces food intake and body weight gain without affecting the insulin sensitivity index measured by minimal modeling in obese Zucker rats. food intake; insulin sensitivity; minimal modeling; obesity

Recent studies have suggested that sensory nerves may influence insulin secretion and action. The present study investigated the effects of resiniferatoxin (RTX) inactivation of sensory nerves (desensitization) on oral glucose tolerance, insulin secretion and whole body insulin sensitivity in the glucose intolerant, hyperinsulinemic, and insulin-resistant obese Zucker rat. After RTX treatment (0.05 mg/kg RTX sc given at ages 8, 10, and 12 wk), fasting plasma insulin was reduced (P < 0.0005), and oral glucose tolerance was improved (P < 0.005). Pancreas perfusion showed that baseline insulin secretion (7 mM glucose) was lower in RTX-treated rats (P = 0.01). Insulin secretory responsiveness to 20 mM glucose was enhanced in the perfused pancreas of RTX-treated rats (P < 0.005) but unaffected in stimulated, isolated pancreatic islets. At the peak of spontaneous insulin resistance in the obese Zucker rat, insulin sensitivity was substantially improved after RTX treatment, as evidenced by higher glucose infusion rates (GIR) required to maintain euglycemia during a hyperinsulinemic euglycemic (5 mU * [kg.sup.-1] * [min.sup.-1]) clamp (GI[R.sub.60-120 min] 5.97 [+ or -] 0.62 vs. 11.65 [ + or -] 0.83 mg * [kg.sup.-l] * [min.sup.-1] in RTX-treated rats, P = 0.003). In conclusion, RTX treatment and, hence, sensory nerve desensitization of adult male obese Zucker rats improved oral glucose tolerance by enhancing insulin secretion, and, in particular, by improving insulin sensitivity. capsaicin; hyperinsulinemic englycemic clamp; obesity

Glucagon has a short plasma [t.sub.1/2] in vivo, with renal extraction playing a major role in its elimination. Glucagon is degraded by neutral endopeptidase (NEP) 24.11 in vitro, but the physiological relevance of NEP 24.11 in glucagon metabolism is unknown. Therefore, the influence of candoxatril, a selective NEP inhibitor, on plasma levels of endogenous and exogenous glucagon was examined in anesthetized pigs. Candoxatril increased endogenous glucagon concentrations, from 6.3 [+ or -] 2.5 to 20.7 [+ or -] 6.3 pmol/l [COOH-terminal (C)-RIA, P < 0.05]. During glucagon infusion, candoxatril increased the [t.sub.1/2] determined by C-RIA (from 3.0 [+ or -] 0.5 to 17.0 [+ or -] 2.5 min, P < 0.005) and midregion (M)-RIA (2.8 [+ or -] 0.5 to 17.0 [+ or -] 3.0 min, P < 0.01) and reduced metabolic clearance rates (MCR; 19.1 [+ or -] 3.2 to 9.4 [+ or -] 2.0 ml*[kg.sup.-1]*[min.sup.-1], P < 0.02, C-RIA; 19.2 [+ or -] 4.8 to 9.0 [+ or -] 2.3 ml*[kg.sup.-1]*[min.sup.-1], P < 0.05, M-RIA). However, neither [t.sub.1/2] nor MCR determined by N[H.sub.2]-terminal (N)-RIA were significantly affected ([t.sub.1/2], 2.7 [+ or -] 0.4 to 4.5 [+ or -] 1.6 min; MCR, 30.3 [+ or -] 6.4 to 28.5 [+ or -] 9.0 ml*[kg.sup.-1]*[min.sup.-1]), suggesting that candoxatril had no effect on N[H.sub.2]-terminal degradation but leads to the accumulation of N[H.sub.2]-terminally truncated forms of glucagon. Determination of arteriovenous glucagon concentration differences revealed that renal glucagon extraction was reduced (but not eliminated) by candoxatril (from 40.4 [+ or -] 3.8 to 18.6 [+ or -] 4.1%, P < 0.02, C-RIA; 29.2 [+ or -] 3.1 to 14.7 [+ or -] 2.2%, P < 0.02, M-RIA; 26.5 [+ or -] 4.0 to 19.7 [+ or -] 3.5%, P < 0.06, N-RIA). Femoral extraction was reduced by candoxatril when determined by C-RIA (from 22.7 [+ or -] 2.4 to 8.0 [+ or -] 5.1%, P < 0.05) but was not changed significantly when determined using M- or N-RIAs (10.0 [+ or -] 2.8 to 4.7 [+ or -] 3.7%, M-RIA; 10.5 [+ or -] 2.5 to 7.8 [+ or -] 4.2%, N-RIA). This study provides evidence that NEP 24.11 is an important mediator of the degradation of both endogenous and exogenous glucagon in vivo. candoxatril; peptide; enzyme inhibition

Inhibition of ATP-sensitive [K.sup.+] ([K.sub.ATP]) channels by an increase in the ATP/ADP ratio and the resultant membrane depolarization are considered essential in the process leading to insulin release (IR) from pancreatic [beta]-cells stimulated by glucose. It is therefore surprising that mice lacking the sulfonylurea type 1 receptor (SUR[1.sup.-/-]) in [3-cells remain euglycemic even though the knockout is expected to cause hypoglycemia. To complicate matters, isolated islets of SUR[1.sup.-/-] mice secrete little insulin in response to high glucose, which extrapolates to hyperglycemia in the intact animal. It remains thus unexplained how euglycemia is maintained. In recognition of the essential role of neural and endocrine regulation of IR, we evaluated the effects of acetylcholine (ACh) and glucagon-like peptide-1 (GLP-1) on IR and free intracellular Ca2+ concentration ([[Ca.sup.2+].sub.i]) of freshly isolated or cultured islets of SUR[1.sup.-/-] mice and B6D2F1 controls (SUR[1.sup.+/+]). IBMX, a phosphodiesterase inhibitor, was also used to explore cAMP-dependent signaling in IR. Most striking, and in contrast to controls, SUR[1.sup.-/-] islets are hypersensitive to ACh and IBMX, as demonstrated by a marked increase of IR even in the absence of glucose. The hypersensitivity to ACh was reproduced in control islets by depolarization with the SUR1 inhibitor glyburide. Pretreatment of perifused SUR[1.sup.-/-] islets with ACh or IBMX restored glucose stimulation of IR, an effect expectedly insensitive to diazoxide. The calcium channel blocker verapamil reduced but did not abolish ACh-stimulated IR, supporting a role for intracellular [Ca.sup.2+] stores in stimulus-secretion coupling. The effect of ACh on IR was greatly potentiated by GLP-1 (10 nM). ACh caused a dose-dependent increase in [[Ca.sup.2+].sub.i] at 0.1-1 [micro]M or biphasic changes (an initial sharp increase in [[Ca.sup.2+].sub.i] followed by a sustained phase of low [[Ca.sup.2+].sub.i]) at 1-100 [micro]M. The latter effects were observed in substrate-free medium or in the presence of 16.7 mM glucose. We conclude that SUR1 deletion depolarizes the [beta]-cells and markedly elevates basal [[Ca.sup.2+].sub.i]. Elevated [[Ca.sup.2+].sub.i] in turn sensitizes the [beta]-cells to the secretory effects of ACh and IBMX. Priming by the combination of high [[Ca.sup.2+].sub.i], ACh, and GLP-1 restores the defective glucose responsiveness, precluding the development of diabetes but not effectively enough to cause hyperinsulinemic hypoglycemia. calcium

NN2211 is a long-acting, metabolically stable glucagon-like peptide-1 (GLP-1) derivative designed for once daily administration in humans. NN2211 dose dependently reduced the glycemic levels in ob/ob mice, with antihyperglycemic activity still evident 24 h postdose. Apart from an initial reduction in food intake, there were no significant differences between NN2211 and vehicle treatment, and body weight was not affected. Histological examination revealed that [beta]-cell proliferation and mass were not increased significantly in ob/ob mice with NN2211, although there was a strong tendency for increased proliferation. In db/db mice, exendin-4 and NN2211 decreased blood glucose compared with vehicle, but NN2211 had a longer duration of action. Food intake was lowered only on day 1 with both compounds, and body weight was unaffected. [beta]-Cell proliferation rate and mass were significantly increased with NN2211, but with exendin-4, only the [beta]-cell proliferation rate was significantly increased. In conclusion, NN2211 reduced blood glucose after acute and chronic treatment in ob/ob and db/db mice and was associated with increased [beta]-cell mass and proliferation in db/db mice. NN2211 is currently in phase 2 clinical development. incretin hormones; diabetes; animal models; glucagon-like peptide-1