FIG. 1.

Metabolic response to a threefold increase in portal vein insulin infusion in dogs maintained on a pancreatic clamp (compared with basal insulin–infused controls). A–D: Circulating insulin, glucagon, and NEFA levels. E–J: Glucose flux parameters. Euglycemia was maintained (E) with similar rates of glucose infusion (F) between groups. Threefold insulin caused the suppression of EGP (G) and NHGB (H). The alteration in NHGB was a function of suppressed net hepatic glycogenolytic flux (I) with no effect on net hepatic gluconeogenic flux (J). Values are means ± SEM; n = 5 in each hyperinsulinemic group and n = 7 in the basal insulin control group. There were no significant differences among hyperinsulinemic groups in any parameter when brain insulin action was blocked. During the hyperinsulinemic period insulin, NEFA, glucose infusion rate, EGP, net hepatic glucose balance, and net hepatic glycogenolytic flux differed (P < 0.05) in those groups from their basal period values and compared with the basal insulin group.