The role of insulin and glucagon in regulating glucose turnover in dogs during exercise.
During exercise the flux of glucose is regulated so that the increased demand of glucose by the muscle is met by a corresponding increased release of glucose by the liver; plasma glucose concentration does not change markedly, while glucose turnover increases. These precise regulatory mechanisms can be studied by quantitative isotope dilution methods; measurements of plasma glucose concentrations do not necessarily reflect any changes in glucose fluxes. Insulin is considered to be an important regulatory hormone during exercise. Its concentration decreases during exercise in part because of a decrease in insulin secretion by the pancreas and in part because the removal of insulin is increased. This conclusion was reached because insulin concentration in plasma decreased both in normal and in depancreatized insulin-infused dogs. A sudden decrease of portal insulin concentration facilitates glycogenolysis and gluconeogenesis in the liver. At the same time blood flow decreases in those areas which are inactive during exercise such as the splanchnic beds, while increased blood flow and opening of the capillary beds increases the total amount of insulin perfusing the muscle. Therefore, even in presence of low insulin concentration in plasma the insulin supply to the working muscle can presumably be maintained at an adequate level. We considered that exercise changes the distribution of insulin in relation to the liver and the muscle; such a distribution pattern may represent an important physiological regulatory mechanism. The question whether glucagon is essential in regulating glucose production during exercise could not be resolved because depancreatized insulin-infused dogs had essentially normal plasma concentrations of immunoreactive glucagon. Glucagon concentration increases during strenuous but not during moderate exercise of normal dogs. This increase is apparently not indispensable because during strenuous exercise depancreatized insulin-infused dogs did not increase IRG
D000818:Animals; D001786:Blood Glucose; D002250:Carbon Radioisotopes; D003920:Diabetes Mellitus / Q000378:metabolism; D004285:Dogs; D005934:Glucagon / Q000008:administration & dosage / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D007003:Hypoglycemia / Q000453:epidemiology; D007263:Infusions, Parenteral; D007328:Insulin / Q000008:administration & dosage / Q000502:physiology*; D010180:Pancreatectomy; D005082:Physical Exertion
D001786:Blood Glucose; D002250:Carbon Radioisotopes; D007328:Insulin; D005934:Glucagon; D005947:Glucose