NEUROPEPTIDE-Y EXPRESSION AND REGULATION IN A DIFFERENTIATED RAT INSULIN-SECRETING CELL-LINE

Neuropeptide-Y (NPY) is a 36-amino acid peptide known to inhibit gluco se-stimulated insulin secretion in various animal models in vitro and in vivo. NPY is thought to be one of the mediators of sympathetic acti on in the pancreas through nerve endings surrounding the islets, and i t has recently been shown to be synthesized within the islets of Lange rhans. To elucidate the potential role of NPY in the endocrine pancrea s, we studied the expression and regulation of NPY secretion in a rat insulinoma cell line (INS-1). NPY mRNA and peptide are highly expresse d and secreted by INS-1 cells. NPY levels were determined by a sensiti ve and specific two-site amplified enzyme-linked immunosorbent assay. Incubation of INS-1 cells with various glucose concentrations did not modify NPY secretion; however, stimulation of adenylate cyclase by for skolin induced a dose- and time-dependent increase in NPY release in t he medium. The glucagon-like peptide-I-(7-36) amide (GLP-1), a known g luco-incretin in humans, induced at low concentration (10(-9) m) a sim ilar expression of NPY mRNA and peptide secretion in INS-1 cells. On t he other hand, the inhibition of cAMP accumulation by the alpha2-adren ergic agonist clonidine decreased NPY secretion. In conclusion, 1) hig h levels of gene expression and secretion of NPY are found in a rat in sulinoma cell line (INS-1). 2) Accumulation of cAMP induced by forskol in or a gluco-incretin (GLP-1) induces a further increase in NPY gene expression and release. 3) NPY secretion is not modulated by low or hi gh glucose concentrations in the medium. 4) Induction of NPY, a known inhibitor of insulin secretion, may represent a novel counterregulator y mechanism of insulin secretion, limiting the stimulatory effect of G LP-1 on insulin secretion.