Effects of insulin on triglyceride and free fatty acid metabolism in man

Abstract

The response of triglyceride and freefatty acid (FFA) concentrations were compared after acute or prolonged mild hypoglycemia was induced by insulin in normal subjects. Intravenously administered glucagon-free insulin (0.12 units/Kg.) caused acute falls in the levels of plasma glucose and FFA, with secondary rises in each moiety. Concomitantly, no consistent alteration was noted in plasma triglycerides during the induction of hypoglycemia, during the rebound phase, or 24 hours after the acute induction of hypoglycemia. During constant infusions of 0.01–0.02 units of insulin/Kg./hour for periods of 5–8 hours, plasma glucose remained suppressed. After initial decreases rebounds in FFA levels were observed during the infusions, but especially after discontinuing the infusions. Plasma triglycerides declined in 3 of 7 patients during the infusions, and triglyceride levels of all subjects were depressed to 55–84 per cent of control values on the morning after the infusions. During a constant infusion of palmitic acid-1-C14, acute and sustained insulin administration uniformly suppressed the rate of appearance of C14 label in plasma triglycerides. The mechanisms of insulin action in diminishing triglyceride levels have not been defined. The striking rebound in FFA levels following the cessation of the insulin infusions is presented as possible evidence in vivo of the inhibition, by insulin, of hormonally mediated lipolysis The response of triglyceride and freefatty acid (FFA) concentrations were compared after acute or prolonged mild hypoglycemia was induced by insulin in normal subjects. Intravenously administered glucagon-free insulin (0.12 units/Kg.) caused acute falls in the levels of plasma glucose and FFA, with secondary rises in each moiety. Concomitantly, no consistent alteration was noted in plasma triglycerides during the induction of hypoglycemia, during the rebound phase, or 24 hours after the acute induction of hypoglycemia. During constant infusions of 0.01–0.02 units of insulin/Kg./hour for periods of 5–8 hours, plasma glucose remained suppressed. After initial decreases rebounds in FFA levels were observed during the infusions, but especially after discontinuing the infusions. Plasma triglycerides declined in 3 of 7 patients during the infusions, and triglyceride levels of all subjects were depressed to 55–84 per cent of control values on the morning after the infusions. During a constant infusion of palmitic acid-1-C14, acute and sustained insulin administration uniformly suppressed the rate of appearance of C14 label in plasma triglycerides. The mechanisms of insulin action in diminishing triglyceride levels have not been defined. The striking rebound in FFA levels following the cessation of the insulin infusions is presented as possible evidence in vivo of the inhibition, by insulin, of hormonally mediated lipolysis