Potential for Gut Peptide-Based Therapy in Postprandial Hypotension.

Postprandial hypotension (PPH) is an important and under-recognised disorder resulting from inadequate compensatory cardiovascular responses to meal-induced splanchnic blood pooling. Current approaches to management are suboptimal. Recent studies have established that the cardiovascular response to a meal is modulated profoundly by gastrointestinal factors, including the type and caloric content of ingested meals, rate of gastric emptying, and small intestinal transit and absorption of nutrients. The small intestine represents the major site of nutrient-gut interactions and associated neurohormonal responses, including secretion of glucagon-like peptide-1, glucose-dependent insulinotropic peptide and somatostatin, which exert pleotropic actions relevant to the postprandial haemodynamic profile. This review summarises knowledge relating to the role of these gut peptides in the cardiovascular response to a meal and their potential application to the management of PPH.

Gastrointestinal Mechanisms Underlying the Cardiovascular Effect of Metformin.

Metformin, the most widely prescribed drug therapy for type 2 diabetes, has pleiotropic benefits, in addition to its capacity to lower elevated blood glucose levels, including mitigation of cardiovascular risk. The mechanisms underlying the latter remain unclear. Mechanistic studies have, hitherto, focused on the direct effects of metformin on the heart and vasculature. It is now appreciated that effects in the gastrointestinal tract are important to glucose-lowering by metformin. Gastrointestinal actions of metformin also have major implications for cardiovascular function. This review summarizes the gastrointestinal mechanisms underlying the action of metformin and their potential relevance to cardiovascular benefits.

Metformin attenuates the postprandial fall in blood pressure in type 2 diabetes.

Metformin has been shown to modulate the cardiovascular response to intraduodenal glucose in patients with type 2 diabetes (T2DM), and may have the capacity to regulate postprandial blood pressure (BP), which is often inadequately compensated in T2DM, resulting in postprandial hypotension. In the present study, we evaluated the acute effects of metformin on the BP and heart rate (HR) responses to oral glucose in patients with T2DM. Ten diet-controlled T2DM patients were evaluated on two occasions in a double-blind, randomized, crossover design. Participants received either metformin 1 g or saline (control) intraduodenally 60 minutes before ingesting a 50 g glucose drink labelled with 150 mg 13 C-acetate. BP, HR, plasma glucagon-like peptide-1 (GLP-1) and gastric emptying (breath test) were evaluated over 180 minutes. Systolic and diastolic BP decreased and HR increased after oral glucose (P < 0.001 for all) on both days. Metformin attenuated the fall in systolic BP (P < 0.001), increased plasma GLP-1 concentrations (P < 0.05) and slowed gastric emptying (P < 0.05) without significantly affecting diastolic BP or HR. In conclusion, metformin acutely attenuates the hypotensive response to oral glucose, associated with augmented GLP-1 secretion and delayed gastric emptying, effects potentially relevant to its favourable cardiovascular profile.

Comparative effects of proximal and distal small intestinal administration of metformin on plasma glucose and glucagon-like peptide-1, and gastric emptying after oral glucose, in type 2 diabetes.

AIMS: The gastrointestinal tract, particularly the lower gut, may be key to the anti-diabetic action of metformin. We evaluated whether administration of metformin into the distal, vs the proximal, small intestine would be more effective in lowering plasma glucose by stimulating glucagon-like pepetide-1 (GLP-1) and/or slowing gastric emptying (GE) in type 2 diabetes (T2DM). MATERIALS AND METHODS: Ten diet-controlled T2DM patients were studied on three occasions. A transnasal catheter was positioned with proximal and distal infusion ports located 13 and 190 cm beyond the pylorus, respectively. Participants received infusions of (a) proximal + distal saline (control), (b) proximal metformin (1000 mg) + distal saline or (c) proximal saline + distal metformin (1000 mg) over 5 minutes, followed 60 minutes later by a glucose drink containing 50 g glucose and 150 mg 13 C-acetate. "Arterialized" venous blood and breath samples were collected over 3 hours for measurements of plasma glucose, GLP-1, insulin and glucagon, and GE, respectively. RESULTS: Compared with control, both proximal and distal metformin reduced plasma glucose and augmented GLP-1 responses to oral glucose comparably (P < 0.05 each), without affecting plasma insulin or glucagon. GE was slower after proximal metformin than after control (P < 0.05) and tended to be slower after distal metformin, without any difference between proximal and distal metformin. CONCLUSIONS: In diet-controlled T2DM patients, glucose-lowering via a single dose of metformin administered to the upper and lower gut was comparable and was associated with stimulation of GLP-1 and slowing of GE. These observations suggest that the site of gastrointestinal administration is not critical to the glucose-lowering capacity of metformin.