EFFECTS OF GLUCAGON-LIKE PEPTIDE-1 (GLP-1) IN RINM5F INSULINOMA CELLS- STIMULATION OF INSULIN-SECRETION, INSULIN CONTENT, AND INSULIN-RECEPTOR BINDING

Glucagon-like peptide-1 (GLP-1) is the major incretin hormone from the distal small intestine which stimulates basal and glucose-induced ins ulin secretion. Using the rat insulinoma cell line RINm5F (Gazdar et a l. 1980) we investigated the effects of GLP-1 on insulin secretion, in sulin content, and insulin receptor binding. During a 1 hour incubatio n, GLP-1 [1 nM] stimulated insulin secretion 2-fold (p < 0.01 vs contr ols). Incubating RINm5F for 24 h with GLP-1 [1 nM], a 1.6-fold higher cellular insulin content was observed (p < 0.01 vs controls). Moreover , GLP-1 induced a 2-fold higher capacity and a 15-fold higher affinity of I-125-insulin binding on the cell surface (p < 0.01 vs controls). Glucagon, known as a potent stimulator of insulin secretion, yielded a similar effect only in 1,000-fold higher concentrations, whereas the intracellular insulin content as well as insulin receptor binding was not increased. Taken together, in RINm5F insulinoma cells GLP-1 potent ly stimulates insulin secretion and insulin content, and improves insu lin receptor binding.