The effects of glucagon and glucagon-(1-21)-peptide on antroduodenal motility in healthy volunteers

Intestinal motor activity, endoluminal motion and transit

A programme for evaluation of intestinal motility has been recently developed based on endoluminal image analysis using computer vision methodology and machine learning techniques. Our aim was to determine the effect of intestinal muscle inhibition on wall motion, dynamics of luminal content and transit in the small bowel. Fourteen healthy subjects ingested the endoscopic capsule (Pillcam, Given Imaging) in fasting conditions. Seven of them received glucagon (4.8 microg kg(-1) bolus followed by a 9.6 microg kg(-1) h(-1) infusion during 1 h) and in the other seven, fasting activity was recorded, as controls. This dose of glucagon has previously shown to inhibit both tonic and phasic intestinal motor activity. Endoluminal image and displacement was analyzed by means of a computer vision programme specifically developed for the evaluation of muscular activity (contractile and non-contractile patterns), intestinal contents, endoluminal motion and transit. Thirty-minute periods before, during and after glucagon infusion were analyzed and compared with equivalent periods in controls. No differences were found in the parameters measured during the baseline (pretest) periods when comparing glucagon and control experiments. During glucagon infusion, there was a significant reduction in contractile activity (0.2 +/- 0.1 vs 4.2 +/- 0.9 luminal closures per min, P < 0.05; 0.4 +/- 0.1 vs 3.4 +/- 1.2% of images with radial wrinkles, P < 0.05) and a significant reduction of endoluminal motion (82 +/- 9 vs 21 +/- 10% of static images, P < 0.05). Endoluminal image analysis, by means of computer vision and machine learning techniques, can reliably detect reduced intestinal muscle activity and motion.

Histologic distribution of insulin and glucagon receptors

Insulin and glucagon are the hormonal polypeptides secreted by the B and A cells of the endocrine pancreas, respectively. Their major physiologic effects are regulation of carbohydrate metabolism, but they have opposite effects. Insulin and glucagon have various physiologic roles, in addition to the regulation of carbohydrate metabolism. The physiologic effects of insulin and glucagon on the cell are initiated by the binding of each hormone to receptors on the target cells. Morphologic studies may be useful for relating biochemical, physiologic, and pharmacologic information on the receptors to an anatomic background. Receptor radioautography techniques using radioligands to label specific insulin and glucagon receptors have been successfully applied to many tissues and organs. In this review, current knowledge of the histologic distribution of insulin and glucagon receptors is presented with a brief description of receptor radioautography techniques.

Effects of glucagon on postprandial carbohydrate metabolism in nondiabetic humans

The present experiments sought to determine whether glucagon concentrations mimicking those observed in people with diabetes mellitus alter postprandial carbohydrate metabolism in nondiabetic humans. We measured the gastric emptying of solids and liquids, the systemic rate of appearance of ingested glucose, and endogenous glucose production either when postprandial suppression of glucagon was prevented by infusing glucagon at a rate of 0.65 ng/kg/min, when postprandial glucagon concentrations were elevated by infusing glucagon at a rate of 3.0 ng/kg/min, or when postprandial suppression of glucagon was permitted by infusion of saline. Despite marked differences in glucagon concentrations, postprandial glucose and insulin concentrations did not differ on any occasion. Although gastric emptying of liquids and solids was comparable on all three occasions, the high-dose, but not the low-dose, glucagon infusion caused a slight delay in the systemic appearance of ingested glucose and a significant decrease (P < .01) in postprandial D-xylose concentrations, suggesting a delay in carbohydrate absorption. However, this was offset by an increase (P < .05) in endogenous glucose production, resulting in no difference in postprandial glucose appearance. We conclude that in the absence of insulin deficiency, neither a lack of suppression of glucagon nor an elevation of glucagon to levels encountered in uncontrolled diabetes mellitus cause postprandial hyperglycemia in nondiabetic humans.

Mechanism of accelerated gastric emptying of liquids and hyperglycemia in patients with type II diabetes mellitus

BACKGROUND & AIMS

The roles of hyperglycemia in diabetic gastroparesis and gastric delivery in postprandial hyperglycemia of diabetic patients are unclear. The aims of this study were to assess gastric emptying and its relation to postprandial glucose metabolism in patients with asymptomatic non-insulin-dependent diabetes mellitus (NIDDM) and no autonomic neuropathy and to identify motor mechanisms responsible for any accelerated gastric emptying.

METHODS

Autonomic function, gastric emptying, postprandial glucose metabolism, and hormone levels (glucagon, insulin, cholecystokinin, glucose-dependent insulinotropic polypeptide, neurotensin, and peptide YY) were assessed in healthy volunteers and patients with NIDDM. In a second study, gastric tone and motility were measured in patients with accelerated gastric emptying and in controls.

RESULTS

Gastric emptying of solids did not differ in the two groups, but liquids emptied faster in patients with NIDDM (P < 0.02). The rate of entry of ingested glucose into the systemic circulation was similar, but higher postprandial glucagon and lower insulin concentrations led to greater (P < 0.01) postprandial hepatic glucose release. Levels of other enteropeptides, gastric accommodation, and antral motility were similar, but patients with NIDDM had greater proximal gastric phasic contractions than controls (P < 0.05).

CONCLUSIONS

Excessive hepatic glucose release, not rapid entry of ingested glucose, is the primary cause of postprandial hyperglycemia in patients with NIDDM. Accelerated gastric emptying in patients with nonneuropathic NIDDM is associated with increased proximal stomach phasic contractions.

Glucagon receptor mRNA distribution in rat tissues

In addition to glucagon's role in regulating glucose production from the liver, a number of extrahepatic effects of glucagon have been reported. We have therefore examined various rat tissues for glucagon receptor mRNA expression. In liver, kidney, heart, adipose tissue, spleen, pancreatic islets, ovary, and thymus, glucagon receptor mRNA expression was found to be relatively abundant whereas lower levels were detected in stomach, small intestine, adrenal gland, thyroid, and skeletal muscle. The presence of glucagon receptor mRNA in tissues known to be responsive to glucagon suggests that these effects are mediated by specific glucagon receptors. Furthermore, the finding of glucagon receptor mRNA in the spleen, thymus, thyroid, adrenal gland, ovary, and skeletal muscle, where glucagon is not generally considered to act, indicates that there may be novel actions of glucagon that have yet to be determined.