Load-dependent effects of duodenal glucose on glycemia, gastrointestinal hormones, antropyloroduodenal motility, and energy intake in healthy men

Gastric emptying is a major determinant of glycemia, gastrointestinal hormone release, and appetite. We determined the effects of different intraduodenal glucose loads on glycemia, insulinemia, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and cholecystokinin (CCK), antropyloroduodenal motility, and energy intake in healthy subjects. Blood glucose, plasma hormone, and antropyloroduodenal motor responses to 120-min intraduodenal infusions of glucose at 1) 1 ("G1"), 2) 2 ("G2"), and 3) 4 ("G4") kcal/min or of 4) saline ("control") were measured in 10 healthy males in double-blind, randomized fashion. Immediately after each infusion, energy intake at a buffet meal was quantified. Blood glucose rose in response to all glucose infusions (P < 0.05 vs. control), with the effect of G4 and G2 being greater than that of G1 (P < 0.05) but with no difference between G2 and G4. The rises in insulin, GLP-1, GIP, and CCK were related to the glucose load (r > 0.82, P < 0.05). All glucose infusions suppressed antral (P < 0.05), but only G4 decreased duodenal, pressure waves (P < 0.01), resulted in a sustained stimulation of basal pyloric pressure (P < 0.01), and decreased energy intake (P < 0.05). In conclusion, variations in duodenal glucose loads have differential effects on blood glucose, plasma insulin, GLP-1, GIP and CCK, antropyloroduodenal motility, and energy intake in healthy subjects. These observations have implications for strategies to minimize postprandial glycemic excursions in type 2 diabetes.     

Role of 5-hydroxytryptamine mechanisms in mediating the effects of small intestinal glucose on blood pressure and antropyloroduodenal motility in older subjects

Postprandial hypotension is an important clinical problem, particularly in the elderly. 5-Hydroxytryptamine3 (5-HT3) mechanisms may be important in the regulation of splanchnic blood flow and blood pressure (BP), and in mediating the effects of small intestinal nutrients on gastrointestinal motility. The aims of this study were to evaluate the effects of the 5-HT3 antagonist granisetron on the BP, heart rate (HR), and antropyloroduodenal (APD) motility responses to intraduodenal glucose in healthy older subjects. Ten subjects (5 male, 5 female, aged 65-76 yr) received an intraduodenal glucose infusion (3 kcal/min) for 60 min (t = 0-60 min), followed by intraduodenal saline for a further 60 min (t = 60-120 min) on 2 days. Granisetron (10 microg/kg) or control (saline) was given intravenously at t = -25 min. BP (systolic and diastolic), HR, and APD pressures were measured. Pressure waves in the duodenal channel closest ("local") to the infusion site were quantified separately. During intraduodenal glucose, there were falls in systolic and diastolic BP and a rise in HR (P < 0.0001 for all); granisetron had no effect on these responses. Granisetron suppressed the number and amplitude (P < 0.05 for both) of local duodenal pressures during intraduodenal glucose. Otherwise, the effects of intraduodenal glucose on APD motility did not differ between study days. We conclude that in healthy older subjects, 5-HT3 mechanisms modulate the local duodenal motor effects of, but not the cardiovascular responses to, small intestinal glucose.     

Functional interactions between Prp8, Prp18, Slu7, and U5 snRNA during the second step of pre-mRNA splicing

After the second transesterification step of pre-mRNA splicing, the Prp22 helicase catalyzes release of spliced mRNA by disrupting contacts in the spliceosome that likely involve Prp8. Mutations at Arg1753 in Prp8, which suppress helicase-defective prp22 mutants, elicit temperature-sensitive growth phenotypes, indicating that interactions in the spliceosome involving Prp8-R1753 might be broken prematurely at 37 degrees C. Here we report that mutations in loop I of the U5 snRNA or in Prp18 can suppress the temperature-sensitive prp8-R1753 mutants. The same gain-of-function PRP18 alleles can also alleviate the growth phenotypes of multiple slu7-ts mutants, indicating a functional link between Prp8 and the second step splicing factors Prp18 and Slu7. These findings, together with the demonstration that changes at Arg1753 in Prp8 impair step 2 of pre-mRNA splicing in vitro, are consistent with a model in which (1) Arg1753 plays a role in stabilizing U5/exon interactions prior to exon joining and (2) these contacts persist until they are broken by the helicase Prp22.     

Role of nitric oxide mechanisms in gastric emptying of, and the blood pressure and glycemic responses to, oral glucose in healthy older subjects

The primary aims of this study were to evaluate the effects of the nitric oxide (NO) synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) on gastric emptying (GE) of, and the blood pressure (BP), glycemic, insulin, and incretin responses to, oral glucose in older subjects. Eight healthy subjects (4 males and 4 females, aged 70.9 +/- 1.3 yr) were studied on two separate days, in double-blind, randomized order. Subjects received an intravenous infusion of either l-NAME (180 mug.kg(-1).h(-1)) or saline (0.9%) at a rate of 3 ml/min for 150 min. Thirty minutes after the commencement of the infusion (0 min), subjects consumed a 300-ml drink containing 50 g glucose labeled with 20 MBq (99m)Tc-sulfur colloid, while sitting in front of a gamma camera. GE, BP (systolic and diastolic), heart rate (HR), blood glucose, plasma insulin, and incretin hormones, glucose-dependant insulinotropic-polypeptide (GIP), and glucagon-like peptide-1 (GLP-1), were measured. l-NAME had no effect on GE, GIP, and GLP-1. Between -30 and 0 min l-NAME had no effect on BP or HR. After the drink (0-60 min), systolic and diastolic BP fell (P < 0.05) and HR increased (P < 0.01) during saline; these effects were attenuated (P < 0.001) by l-NAME. Blood glucose levels between 90 and 150 min were higher (P < 0.001) and plasma insulin were between 15 and 150 min less (P < 0.001) after l-NAME. The fall in BP, increase in HR, and stimulation of insulin secretion by oral glucose in older subjects were mediated by NO mechanisms by an effect unrelated to GE or changes in incretin hormones.     

Alterations in carbohydrate metabolism in response to short-term dietary carbohydrate restriction

Dietary carbohydrate restriction (CR) presents a challenge to glucose homeostasis. Despite the popularity of CR diets, little is known regarding the metabolic effects of CR. The purpose of this study was to examine changes in whole body carbohydrate oxidation, glucose availability, endogenous glucose production, and peripheral glucose uptake after dietary CR, without the confounding influence of a negative energy balance. Postabsorptive rates of glucose appearance in plasma (R(a); i.e., endogenous glucose production) and disappearance from plasma (R(d); i.e., glucose uptake) were measured using isotope dilution methods after a conventional diet [60% carbohydrate (CHO), 30% fat, and 10% protein; kcals = 1.3 x resting energy expenditure (REE)] and after 2 days and 7 days of CR (5% CHO, 60% fat, and 35% protein; kcals = 1.3 x REE) in eight subjects (means +/- SE; 29 +/- 4 yr; BMI 24 +/- 1 kg/m(2)) during a 9-day hospital visit. Postabsorptive plasma glucose concentration was reduced (P = 0.01) after 2 days but returned to prediet levels the next day and remained at euglycemic levels throughout the diet (5.1 +/- 0.2, 4.3 +/- 0.3, and 4.8 +/- 0.4 mmol/l for prediet, 2 days and 7 days, respectively). Glucose R(a) and glucose R(d) were reduced to below prediet levels (9.8 +/- 0.6 micromol x kg(-1) x min(-1)) after 2 days of CR (7.9 +/- 0.3 micromol x kg(-1) x min(-1)) and remained suppressed after 7 days (8.3 +/- 0.4 micromol x kg(-1) x min(-1); both P < 0.001). A greater suppression in carbohydrate oxidation, compared with the reduction in glucose R(d), led to an increased (all P 相似文献   

Synthesis and human NKT cell stimulating properties of 3-O-sulfo-alpha/beta-galactosylceramides

Two novel hybrid molecules 3-O-sulfo-alpha/beta-galactosylceramide 3 and 4, which are derived from an immunostimulatory agent alpha-GalCer 1 and self-glycolipid ligand sulfatide 2, were designed and synthesized. Compound 3 was shown to efficiently stimulate human NKT cells to secret IL-4 and IFN-gamma, with activities similar to 1, suggesting that modification of the 3'-OH position of the galactose moiety with sulfate has no significant effect on NKT cell stimulation. As a comparison, the beta-isomer 4 has no affinity to NKT cells, which demonstrates that the alpha-glycosidic bond of galactosylceramide is crucial to the NKT cells activation.     

Phospholipase C in living cells: activation, inhibition, Ca2+ requirement, and regulation of M current

We have further tested the hypothesis that receptor-mediated modulation of KCNQ channels involves depletion of phosphatidylinositol 4,5-bisphosphate (PIP2) by phosphoinositide-specific phospholipase C (PLC). We used four parallel assays to characterize the agonist-induced PLC response of cells (tsA or CHO cells) expressing M1 muscarinic receptors: translocation of two fluorescent probes for membrane lipids, release of calcium from intracellular stores, and chemical measurement of acidic lipids. Occupation of M1 receptors activates PLC and consumes cellular PIP2 in less than a minute and also partially depletes mono- and unphosphorylated phosphoinositides. KCNQ current is simultaneously suppressed. Two inhibitors of PLC, U73122 and edelfosine (ET-18-OCH3), can block the muscarinic actions completely, including suppression of KCNQ current. However, U73122 also had many side effects that were attributable to alkylation of various proteins. These were mimicked or occluded by prior reaction with the alkylating agent N-ethylmaleimide and included block of pertussis toxin-sensitive G proteins and effects that resembled a weak activation of PLC or an inhibition of lipid kinases. By our functional criteria, the putative PLC activator m-3M3FBS did stimulate PLC, but with a delay and an irregular time course. It also suppressed KCNQ current. The M1 receptor-mediated activation of PLC and suppression of KCNQ current were stopped by lowering intracellular calcium well below resting levels and were slowed by not allowing intracellular calcium to rise in response to PLC activation. Thus calcium release induced by PLC activation feeds back immediately on PLC, accelerating it during muscarinic stimulation in strong positive feedback. These experiments clarify important properties of receptor-coupled PLC responses and their inhibition in the context of the living cell. In each test, the suppression of KCNQ current closely paralleled the expected fall of PIP2. The results are described by a kinetic model.     

Activation of the pro-survival phosphatidylinositol 3-kinase/AKT pathway by transforming growth factor-beta1 in mesenchymal cells is mediated by p38 MAPK-dependent induction of an autocrine growth factor

Transforming growth factor-beta1 (TGF-beta1) is a multifunctional cytokine involved in differentiation, growth, and survival of mesenchymal cells while inhibiting growth/survival of most other cell types. The mechanism(s) of pro-survival signaling by TGF-beta1 in mesenchymal cells is unclear. In this report, we demonstrate that TGF-beta1 protects against serum deprivation-induced apoptosis of mesenchymal cells isolated from patients with acute lung injury and of normal human fetal lung fibroblasts (IMR-90). TGF-beta receptor(s)-activated signaling in these cells involves rapid activation of the Smad and p38 MAPK pathways within minutes of TGF-beta1 treatment followed by a more delayed activation of the pro-survival phosphatidylinositol 3-kinase-protein kinase B (PKB)/Akt pathway. Pharmacological inhibition of p38 MAPK with SB203580 or expression of a p38 kinase-deficient mutant protein inhibits TGF-beta1-induced PKB/Akt phosphorylation. Conditioned medium from TGF-beta1-treated cells rapidly induces PKB/Akt activation in an SB203580- and suramin-sensitive manner, suggesting p38 MAPK-dependent production of a secreted growth factor that activates this pro-survival pathway by an autocrine/paracrine mechanism. Inhibition of the phosphatidylinositol 3-kinase-PKB/Akt pathway blocks TGF-beta1-induced resistance to apoptosis. These results demonstrate the activation of a novel TGF-beta1-activated pro-survival/anti-apoptotic signaling pathway in mesenchymal cells/fibroblasts that may explain cell-specific actions of TGF-beta1 and provide mechanistic insights into its pro-fibrotic and tumor-promoting effects.     

Effect of fatty acid chain length on suppression of ghrelin and stimulation of PYY, GLP-2 and PP secretion in healthy men

We have evaluated the effects of fatty acid chain length on ghrelin, peptide YY (PYY), glucagon-like peptide-2 (GLP-2) and pancreatic polypeptide (PP) secretion and hypothesized that intraduodenal administration of dodecanoic ("C12"), but not decanoic ("C10"), acid would decrease plasma ghrelin and increase PYY, GLP-2 and PP concentrations. Plasma hormone concentrations were measured in seven healthy men during 90-min intraduodenal infusions of: (i) C12, (ii) C10 or (iii) control (rate: 2 ml/min, 0.375 kcal/min for C12/C10) and after a buffet-meal consumed following the infusion. C12 markedly suppressed plasma ghrelin and increased both PYY and GLP-2 (all P < 0.05) compared with control and C10, while C10 had no effect. Both C10 and C12 increased PP concentrations slightly (P < 0.05). We conclude that the effects of intraduodenal fatty acids on ghrelin, PYY and GLP-2 secretion are dependent on their chain length.