Effects of hormones on cyclic AMP release from rat adipose tissue in vitro

Abstract

Lipolysis is regulated, at least in part, by the intracellular level of cyclic AMP [ 1,2] . The effects of several hormones and of lipolytic and antilipolytic agents on CAMP accumulation in adipose tissue and adipocytes have been extensively studied [3-61. Most experiments were carried out with isolated fat cells [4-81. Little attention has been paid to CAMP release from intact adipose tissue [3]. During liver perfusion CAMP is released into the perfusion medium in response to glucagon and to epinephrine [9, lo] . Therefore, we examined to what extent CAMP was released from adipose tissue in response to these lipolytic hormones and whether lipolysis was correlated with CAMP release, which may reflect metabolically available ‘free’ CAMP in the cell [9] . Furthermore, we were interested to find out whether partially purified nonsuppressible insulin-like activity (NSILA-S) which has been shown to exert the same metabolic effects on adipose tissue as insulin (for review see [ 111) affects epinephrine-induced CAMP release. The results of this study show that: 1) Considerable amounts of CAMP are released from adipose tissue only when theophylline is present in addition to lipolytic hormones. After 30 min CAMP, which has accumulated in the medium, rapidly disappears possibly due to enhanced degradation. 2) CAMP release is inhibited by insulin and NSILA-S. 3) Concomitant inhibition by insulin of epinephrine-induced lipolysis and of CAMP release is observed only at low epinephrine concentrations, whereas at higher epinephrine concentrations lipolysis