Glucose kinetics and fatty acids in dogs on matched insulin infusion after glucose load

Abstract

The endogenous insulin secretion of five conscious, depancreatized fasted dogs was replaced by intraportal insulin infusions of 192–263 μU/kg per min to establish whether the release of extra insulin is essential during a glucose tolerance test. Infusion rate of insulin about 200 μU/kg per min was considered to be near basal since it maintained unchanged glucose turnover as well as the plasma concentrations of glucose, free fatty acids (FFA), and immunoreactive insulin (IRI). The glucose tolerance tests of these dogs were then compared to those of six normal and six partially depancreatized dogs. It was found that after an intravenous injection of glucose the depancreatized dogs maintained on portal or peripheral insulin infusion had a 50% decreased exponential slope of the plasma glucose concentration versus time (k). In contrast to the normal dogs, their plasma glucose levels were still elevated but declining 60–140 min after the glucose load. The declining glucose levels were associated with an increased disappearance rate (R d), but there was no inhibition of the rate of glucose production. FFA decreased only slightly after the glucose load. Five days after partial pancreatectomy the dogs reacted to a glucose injection with a lesser output of insulin than normal dogs. Their homeostatic deficiencies with respect to glucose kinetics and FFA response were less marked than in depancreatized dogs maintained on matched insulin infusion. It was concluded that a prompt release of extra insulin is an essential part of the normal homeostatic mechanisms that determine a glucose tolerance curve.