INVESTIGATIONS INTO THE ACTIONS OF GLUCOSE-DEPENDENT INSULINOTROPIC POLYPEPTIDE AND GLUCAGON-LIKE PEPTIDE-1(7-36)AMIDE ON LIPOPROTEIN-LIPASE ACTIVITY IN EXPLANTS OF RAT ADIPOSE-TISSUE

The direct actions of glucose-dependent insulinotropic polypeptide, gl ucagon-like peptide1((7-36))amide and insulin on lipoprotein lipase ac tivity in explants of rat epididymal adipose tissues were investigated . Lipoprotein lipase was extracted into the incubation medium by hepar in release of lipoprotein lipase and measured by fatty acid release fr om a glycerol-triolein emulsion. Insulin and glucose-dependent insulin otropic polypeptide caused a significant stimulation of lipoprotein li pase activity over a dose range of 0.25-4 nmol/L and 4-8 nmol/L, respe ctively. Explants incubated in the presence of both insulin and glucos e-dependent insulinotropic polypeptide (at 0.5 and 4 nmol/L, respectiv ely) showed levels of lipoprotein lipase activity significantly greate r than that seen with either hormone alone. Neither insulin- nor gluco se-dependent insulinotropic. polypeptide-stimulated lipoprotein lipase was modified by the presence of the antibiotic actinomycin-D in the i ncubation medium, indicating that these two hormones exert their actio ns on the pre-existing cellular pool of lipoprotein lipase. Glucagon-l ike polypeptide-1((7-36))amide, over a dose range of 1-8 nmol/L, did n dt stimulate lipoprotein lipase activity. This study indicates that gl ucose-dependent insulinotropic polypeptide, in addition to stimulating insulin secretion, has a direct biological action on adipose tissue a nd in vivo, together with insulin, may promote lipoprotein lipase acti vity postprandially.