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 insulin secretion.  Using the rat insulinoma cell line RINm5F (Gazdar et al.  1980) we investigated the effects of GLP-1 on insulin secretion, insulin content, and insulin receptor binding.  During a 1 hour incubation, GLP-1 [1 nM] stimulated insulin secretion 2-fold (p < 0.01 vs controls).  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 125I-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 potently stimulates insulin secretion and insulin content, and improves insulin receptor binding.