Background-A genetic predisposition for progressive enlargement of thoracic aortic aneurysms leading to type A dissection (TAAD) is inherited in an autosomal-dominant manner in up to 19% of patients, and a number of chromosomal loci have been identified for the condition. Having mapped a TAAD locus to 3p24 -25, we sequenced the gene for transforming growth factor-␤ receptor type II (TGFBR2) to determine whether mutations in this gene resulted in familial TAAD. Methods and Results-We sequenced all 8 coding exons of TGFBR2 by using genomic DNA from 80 unrelated familial TAAD cases. We found TGFBR2 mutations in 4 unrelated families with familial TAAD who did not have Marfan syndrome. Affected family members also had descending aortic disease and aneurysms of other arteries. Strikingly, all 4 mutations affected an arginine residue at position 460 in the intracellular domain, suggesting a mutation "hot spot" for familial TAAD. Despite identical mutations in the families, assessment of linked polymorphisms suggested that these families were not distantly related. Structural analysis of the TGFBR2 serine/threonine kinase domain revealed that R460 is strategically located within a highly conserved region of this domain and that the amino acid substitutions resulting from these mutations will interfere with the receptor's ability to transduce signals. Conclusion-Germline

It has been reported that the artificial sweetener, sucralose, stimulates glucose absorption in rodents by enhancing apical availability of the transporter GLUT2. We evaluated whether exposure of the proximal small intestine to sucralose affects glucose absorption and/or the glycaemic response to an intraduodenal (ID) glucose infusion in healthy human subjects. Ten healthy subjects were studied on two separate occasions in a single-blind, randomised order. Each subject received an ID infusion of sucralose (4 mM in 0·9 % saline) or control (0·9 % saline) at 4 ml/min for 150 min (T ¼ 230 to 120 min). After 30 min (T ¼ 0), glucose (25 %) and its non-metabolised analogue, 3-O-methylglucose (3-OMG; 2·5 %), were co-infused intraduodenally (T ¼ 0 -120 min; 4·2 kJ/min (1 kcal/min)). Blood was sampled at frequent intervals. Blood glucose, plasma glucagonlike peptide-1 (GLP-1) and serum 3-OMG concentrations increased during ID glucose/3-OMG infusion (P,0·005 for each). However, there were no differences in blood glucose, plasma GLP-1 or serum 3-OMG concentrations between sucralose and control infusions. In conclusion, sucralose does not appear to modify the rate of glucose absorption or the glycaemic or incretin response to ID glucose infusion when given acutely in healthy human subjects.3-O-methylglucose: Sodium-dependent GLUT 1: GLUT 2: Glucagon-like peptide-1The mechanisms by which the gut senses nutrients are unclear, and the 'receptor' for detecting luminal carbohydrates has, until recently, been elusive. Recent studies indicate the presence of G-protein-coupled taste receptors, T1R2 and T1R3, and their taste signal transduction partners, the G-protein gustducin and the transient receptor potential ion channel TRPM5, in the mucosa of the mouse and human gastrointestinal tract (1,2) . These receptors, analogous to sweet taste receptors on the tongue, broadly respond to sugars and artificial sweeteners, and among several cell types, they appear to co-localise with glucagon-like peptide-1 (GLP-1)-secreting L cells (3) .It has been reported that the artificial sweetener, sucralose, stimulates the secretion of both GLP-1 and glucose-dependent insulinotrophic polypeptide from the mouse enteroendocrine cell line GLUTag (4) , and it stimulates GLP-1 secretion from the human L cell line NCI-H716 (3) , a response that is blocked by the sweet receptor antagonist, lactisole, and siRNA for a-gustducin (3) . However, we recently demonstrated that sucralose, in two different loads, had no effect on GLP-1, glucose-dependent insulinotrophic polypeptide or insulin secretion, and that it did not elicit any feedback response on gastric emptying in healthy human subjects (5) . While this implies that artificial sweeteners may have no therapeutic benefit in the dietary management of diabetes, other than as a substitute for carbohydrates, it remains possible that sucralose affects small intestinal carbohydrate absorption as a result of its interaction with the sweet taste receptors.Glucose is absorbed from the small intestine through both ...

The short-acting glucagon-like peptide 1 receptor agonist exenatide reduces postprandial glycemia, partly by slowing gastric emptying, although its impact on small intestinal function is unknown. In this study, 10 healthy subjects and 10 patients with type 2 diabetes received intravenous exenatide (7.5 mg) or saline (230 to 240 min) in a double-blind randomized crossover design. Glucose (45 g), together with 5 g 3-O-methylglucose (3-OMG) and 20 MBq 99m Tc-sulfur colloid (total volume 200 mL), was given intraduodenally (t = 0-60 min; 3 kcal/min). Duodenal motility and flow were measured using a combined manometry-impedance catheter and small intestinal transit using scintigraphy. In both groups, duodenal pressure waves and antegrade flow events were fewer, and transit was slower with exenatide, as were the areas under the curves for serum 3-OMG and blood glucose concentrations. Insulin concentrations were initially lower with exenatide than with saline and subsequently higher. Nausea was greater in both groups with exenatide, but suppression of small intestinal motility and flow was observed even in subjects with little or no nausea. The inhibition of small intestinal motor function represents a novel mechanism by which exenatide can attenuate postprandial glycemia.Therapies specifically targeting postprandial glycemia are important in the management of type 2 diabetes, especially in patients with relatively good overall glycemic control (HbA 1c #7.5%; 58 mmol/mol) (1). The rate of gastric emptying is an established determinant of postprandial blood glucose (2), a principle illustrated by "short-acting" glucagonlike peptide 1 (GLP-1) receptor agonists, such as exenatide, where the capacity to slow gastric emptying predominates over the insulinotropic effect in the postprandial setting (3).Small intestinal glucose absorption, predominantly via sodium-glucose cotransporter 1 and GLUT2 transporters, is limited to ;0.5 g/min per 30 cm (2). Interventions that increase the exposure of luminal glucose to the mucosal surface can therefore augment glucose absorption. We previously reported that the anticholinergic agent hyoscine delays the absorption of intraduodenally infused glucose in humans by decreasing small intestinal flow (4), indicating PHARMACOLOGY AND THERAPEUTICSthat modulation of small intestinal motor function can impact substantially on postprandial glycemia. Exogenous GLP-1 has been reported to inhibit both fasting and postprandial duodenal motility in humans (5,6), but its impact on the flow of chyme and on small intestinal transit and glucose absorption have not previously been explored. We therefore examined the effects of the short-acting form of exenatide on small intestinal motor function and glucose absorption in response to an intraduodenal glucose infusion in both healthy subjects and patients with type 2 diabetes. RESEARCH DESIGN AND METHODS SubjectsWe studied 10 healthy subjects and 10 patients with type 2 diabetes managed by diet alone, after obtaining written informed consent (Table 1). None ...

OBJECTIVEGlutamine reduces postprandial glycemia when given before oral glucose. We evaluated whether this is mediated by stimulation of insulin and/or slowing of gastric emptying.RESEARCH DESIGN AND METHODSTen healthy subjects were studied during intraduodenal (ID) infusion of glutamine (7.5 or 15 g) or saline over 30 min, followed by glucose (75 g over 100 min), while recording antropyloroduodenal pressures. Ten patients with type 2 diabetes mellitus (T2DM) were also studied with 15 g glutamine or saline.RESULTSID glutamine stimulated glucagon-like peptide 1 (GLP-1; healthy: P < 0.05; T2DM: P < 0.05), glucose-dependent insulinotropic polypeptide (GIP; P = 0.098; P < 0.05), glucagon (P < 0.01; P < 0.001), insulin (P = 0.05; P < 0.01), and phasic pyloric pressures (P < 0.05; P < 0.05), but did not lower blood glucose (P = 0.077; P = 0.5).CONCLUSIONSGlutamine does not lower glycemia after ID glucose, despite stimulating GLP-1, GIP, and insulin, probably due to increased glucagon. Its capacity for pyloric stimulation suggests that delayed gastric emptying is a major mechanism for lowering glycemia when glutamine is given before oral glucose.

OBJECTIVETo evaluate the natural history of gastric emptying in diabetes.RESEARCH DESIGN AND METHODSThirteen patients with diabetes (12, type 1; 1, type 2) had measurements of gastric emptying, blood glucose levels, glycated hemoglobin, upper gastrointestinal symptoms, and autonomic nerve function at baseline and after 24.7 ± 1.5 years.RESULTSThere was no change in gastric emptying of either solids (% retention at 100 min) (baseline 58.5 ± 5% vs. follow-up 51.9 ± 8%; P = 0.35) or liquids (50% emptying time) (baseline 29.8 ± 3 min vs. follow-up 34.3 ± 6 min; P = 0.37). Gastric emptying of solid at follow-up was related to emptying at baseline (r = 0.56, P < 0.05). At follow-up, blood glucose concentrations were lower (P = 0.006), autonomic function deteriorated (P = 0.03), and gastrointestinal symptoms remained unchanged (P = 0.17).CONCLUSIONSIn unselected patients with diabetes, gastric emptying appears remarkably stable over 25 years.

Diabetic gastroparesis was once thought to be rare, associated with a poor prognosis, and to affect only patients with type 1 diabetes and irreversible autonomic neuropathy. A landmark study conducted by Horowitz et al. and published in JGH in 1986 paved the way for further studies to examine the pathophysiology, natural history and prognosis of diabetic gastroparesis, as well as its optimal management. This review summarizes the developments in knowledge gained over the last~25 years that have led to understanding about normal and disordered gastric emptying in diabetes, with a particular emphasis on the inter-relationship between the rate of gastric emptying and the regulation of blood glucose.

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T100 min, the percentage remaining in the stomach at 100 mins; T50%, the time taken for 50% of the liquid to empty.