Lipolysis and α-aminoisobutyric acid uptake in isolated fat cells effects of insulin and lipolytic agents

Abstract

1. 1. The relationship between lipolysis and the energy-dependent α-aminoisobutyric acid uptake by isolated mouse fat cells has been studied. 2. 2. Stimulation of lipolysis by adrenaline, ACTH or caffeine resulted in a marked inhibition of the net α-aminoisobutyric acid uptake by fat cells. The magnitude of this inhibition was proportional to that of lipolysis. 3. 3. The addition of palmitate or octanoate to the incubation medium mimicked lipolytic agents in decreasing net α-aminoisobutyric acid uptake. These effects were ascribed to an increase in intracellular free fatty acids. 4. 4. In the absence of added glucose, insulin decreased the hormone- or caffeine-induced lipolysis. Concomitantly insulin prevented the drop in α-aminoisobutyric acid uptake induced by these lipolytic agents. 5. 5. It is suggested that a decrease in energy availability and/or production occurs during lipolysis, and that it is partly responsible for the observed inhibition of α-aminoisobutyric acid uptake. In the absence of glucose, insulin is thought to prevent, via its antilipolytic action, such a decrease in energy availability and/or production, thereby preventing the drop in α-aminoisobutyric acid uptake induced by lipolytic agents.