The effects of gastric inhibitory polypeptide and insulin on fatty acid uptake in adipose tissue are not mediated through cyclic AMP in lean and obese Zucker rats.

To determine the mechanism by which gastric inhibitory polypeptide (GIP) and insulin stimulate the in vitro fatty acid incorporation into adipose tissue (FIAT), we measured the cyclic AMP variations and FIAT in epididymal fat pads of lean Fa/-- and obese fa/fa Zucker rats. GIP was used at 1, 2 and 4 ng/ml and insulin at a concentration of 100 microU/ml. There was no significant variation of cAMP when FIAT was stimulated either by GIP, either by insulin or by both hormones. There was no correlation at all between FIAT increases and cAMP levels. We conclude that GIP and insulin act through cAMP independent mechanisms in adipose tissue. The modification by GIP of insulin binding to adipocytes or an easier passage of fatty acids through the membrane could constitute alternative solutions for such mechanisms.