Effects of exogenous glucagon and epinephrine in physiological amounts on the blood levels of free fatty acids and glycerol in dogs

Lack of effect of somatostatin on epinephrine-stimulated glucose production in the dog

The effects of somatostatin on epinephrine-stimulated hepatic glucose production were assessed in the conscious overnight fasted dog. Glucose production was measured using a primed constant infusion of 3-3H-glucose. Two experiments were performed on each of four animals, each experiment consisting of a tracer equilibration period (80 minutes), a control period (40 minutes), and a test period (180 minutes). In the first experiment, epinephrine was infused at 0.08 microgram/kg/min during the test period so that the plasma concentration rose from 138 +/- 4 to 727 +/- 109 pg/mL. In the second experiment two weeks later, epinephrine was again infused (112 +/- 17 to 727 +/- 148 pg/mL) but with somatostatin (0.8 microgram/kg/min) and intraportal replacement amounts of insulin and glucagon. The pancreatic hormones were administered in such a way as to mimic the insulin and glucagon levels observed during epinephrine infusion in the first experiment. In the first experiment, epinephrine caused changes in insulin and glucagon levels at five minutes of plus 9 +/- 1 microU/mL and minus 1 +/- 3 pg/mL, respectively, and averaged plus 6 +/- 2 microU/mL and minus 9 +/- 5 pg/mL over the first hour. Glucose production peaked at 15 minutes (increment of 0.83 +/- 0.24 mg/kg/min) and increased by an average of 0.38 +/- 0.12 mg/kg/min in the first hour. In the second experiment, intraportal replacement of insulin and glucagon during epinephrine infusion resulted in changes in insulin and glucagon levels at five minutes of plus 8 +/- 3 microU/mL and plus 2 +/- 2 pg/mL, respectively, and averaged plus 4 +/- 2 microU/mL and minus 7 +/- 6 pg/mL over the first hour.(ABSTRACT TRUNCATED AT 250 WORDS)

Synergistic interactions of physiologic increments of glucagon, epinephrine, and cortisol in the dog: a model for stress-induced hyperglycemia

To evaluate the role of anti-insulin hormone actions and interactions in the pathogenesis of stress-induced hyperglycemia, the counterregulatory hormones, glucagon, epinephrine, and cortisol were infused alone as well as in double and triple combinations into normal conscious dogs in doses that were designed to simulate changes observed in severe stress. Infusion of glucagon, epinephrine, or cortisol alone produced only mild or insignificant elevations in plasma glucose concentration. In contrast, the rise in plasma glucose produced by combined infusion of any two counterregulatory hormones was 50-215% greater (P < 0.005-0.001) than the sum of the respective individual infusions. Furthermore, when all three hormones were infused simultaneously, the increment in plasma glucose concentration (144+/-2 mg/dl) was two- to fourfold greater than the sum of the responses to the individual hormone infusions or the sum of any combination of double plus single hormone infusion (P < 0.001). Infusion of glucagon or epinephrine alone resulted in a transient rise in glucose production (as measured by [3-(3)H]glucose). While glucagon infusion was accompanied by a rise in glucose clearance, with epinephrine there was a sustained, 20% fall in glucose clearance. When epinephrine was infused together with glucagon, the rise in glucose production was additive, albeit transient. However, the inhibitory effect of epinephrine on glucose clearance predominated, thereby accounting for the exaggerated glycemic response to combined infusion of glucagon and epinephrine. Although infusion of cortisol alone had no effect on glucose production, the addition of cortisol markedly accentuated hyperglycemia produced by glucagon and(or) epinephrine primarily by sustaining the increases in glucose production produced by these hormones. The combined hormonal infusions had no effect on beta-hydroxybutyrate concentration. It is concluded that (a) physiologic increments in glucagon, epinephrine, and cortisol interact synergistically in the normal dog so as to rapidly produce marked fasting hyperglycemia; (b) in this interaction, epinephrine enhances glucagon-stimulated glucose output and interferes with glucose uptake while cortisol sustains elevations in glucose production produced by epinephrine and glucagon; and (c) these data indicate that changes in glucose metabolism in circumstances in which several counterregulatory hormones are elevated (e.g., "stress hyperglycemia") are a consequence of synergistic interactions among these hormones.

Extrapancreatic glucagon and glucagonlike immunoreactivity in depancreatized dogs. A quantitative assessment of secretion rates and anatomical delineation of sources

The anatomical sites and the rates of extrapancreatic secretion of glucagon and of glucagon-like immunoreactivity (GLI) were assessed in dogs 2 h after pancreatectomy by catheterization of the gastrosplenic and mesenteric veins. Glucagon release from the gastrosplenic area approximated one-fourth that of a normal pancreas and rose from 0.25 to 1.0 ng/kg per min during arginine stimulation. Intestinal glucagon secretion was small and did not respond to arginine, suggesting that the stomach is the only important extrapancreatic source of glucagon. Glucagon concentrations attained by gastrosplenic secretion were in close proportion to those obtained during the administration of exogenous glucagon, indicating similar clearance rates of extrapancreatic and pancreatic glucagon, approximating 10 ml/kg per min.GLI secretion (0.3 ng eq/kg per min) was limited to the intestinal area and was transiently stimulated by arginine and exogenous glucagon. Base-line GLI clearance approximated 1 ml/kg per min. No insulin secretion could be detected. Gastrointestinal glucose uptake rose from 0.56 to 2.2 mg/kg per min after glucagon administration suggesting that as much as 10% of total glucose production can be taken up by the gastrointestinal tract. In two dogs both the stomach and pancreas were removed. Intestinal glucagon release remained small and did not increase during arginine administration. By contrast, GLI release was stimulated by both arginine and exogenous glucagon.