Stimulus-secretion coupling of arginine-induced insulin release. Metabolism of l-arginine and l-ornithine in pancreatic islets

Abstract

Exogenous l-arginine and l-ornithine rapidly accumulate in rat pancreatic islets. l-Arginine is converted to l-ornithine and urea. Endogenous or exogenous l-ornithine generates di- and polyamines, the putrescine turnover being faster than that of spermidine and spermine. However, the major pathway for l-ornithine metabolism consists of its transamination to l-glutamaldehyde and further conversion to l-glutamate. The amines and l-glutamate derived from exogenous l-ornithine are incorporated into islet proteins at the intervention of transglutaminase and cycloheximide-sensitive biosynthetic processes, respectively. These findings suggest the hypothesis that the insulinotropic action of l-arginine and l-ornithine could somehow be related to the metabolism of these cationic amino acids in islet cells.