PRESENCE AND CHARACTERIZATION OF GLUCAGON-LIKE PEPTIDE-1 (7-36) AMIDE RECEPTORS IN SOLUBILIZED MEMBRANES OF RAT ADIPOSE-TISSUE

Specific binding of [I-125]glucagon-like peptide-1(7-36)amide ([I-125] GLP-1(7-36)amide) to solubilized rat adipose tissue membranes was found to be dependent on temperature, time, and membrane protein concentration and readily dissociated. GLP-1(1-36)amide, GLP-2, or glucagon (10(-6) M) did not compete with [I-125]GLP-1(7-36)amide binding. Half-maximal binding was achieved with 8 x 10(-10) m unlabeled GLP-1(7-36)amide, and the Scatchard plot revealed the presence of high and low affinity binding sites with K(d) values of approximately 0.6 and 20 nm, respectively. The binding capacity of [I-125]GLP-1(7-36)amide was about 3 times higher than that of [I-125]glucagon, while the high affinity K(d) and the half-maximal binding of the two peptides were similar. The presence and abundance of GLP-1(7-36)amide receptors in fat tissue together with the previous findings that the peptide stimulates glycerol and cAMP production in rat adipocytes (18) and stimulates fatty acid synthesis in explants of rat adipose tissue (28) open the possibility that this insulinotropic intestinal peptide may also be involved in the regulation of lipid metabolism in health and disease.