Glucose dependent insulinotropic polypeptide and glucagon-like peptide-1(7–36)amide: effects on lipoprotein lipase activity

Abstract

GIP (glucose dependent insulinotropic polypeptide) and GLPl(7-36)amide (the major intestinal truncated form of glucagonlike peptide-1) are important stimuli for insulin secretion in the post-prandial hyperglycaemic state [l]. Dietary triglycerides are a potent stimulus for GIP secretion [2]. In-vitro studies have shown that GIP can stimulate both de novo lipogenesis and fatty acid incorporation into rat epididymal adipose tissue [3.4] and increase LPL (lipoprotein lipase) activity in cultured 3T3-LI mouse pre-adipccytes [5]. GLP-1(7-36)amide is also modestly stimulated by fat [6] and can also stimulate de novo lipogenesis P I . Here we present our preliminary findings on the in-vitro action of these two hormones GIP and GLP-1(7-36)amide on LPL activity in rats. Adipose tissue explants (1 1 Smg) were prepared from the epididymal fat pads of rats (200.250g body weight). Explants were cultured in Medium 199, for 2h in the presence of insulin (0-4 nM); GIP (0-8 nM); insulin/GIP (0.5 and 4 nM respectively) or GLP-1(7-36)amide (0-4 nM). After 2h heparin was added to the incubation medium to give a final concentration of 2U/ ml. explants were further incubated for 45 min. Subsequently the medium was removed, assayed for LPL activity and the explants weighed. LPL activity was determined using triolein as substrate according to the method of NdssonEhle & Schotz in the presence of high and low salt [7].