Stimulus-secretion coupling of arginine-induced insulin release. Effect of 2-aminoisobutyric acid upon ornithine decarboxylase activity and insulin secretion.

Recent studies have revealed that, in rat pancreatic islets, exogenous L-arginine or L-ornithine are converted to putrescine, spermidine and spermine. The possible role of polyamine generation in the secretory response of the B-cell to the cationic amino acids was investigated in islets either preincubated for 90 min with 2-aminoisobutyric acid (AIB; 10 mM) or removed from rats injected intraperitoneally with AIB (2.4 mmol) 210 min before sacrifice. Although AIB failed to exert any direct effect upon the secretory response of the islets to either L-arginine or L-ornithine, preincubation of the islets with AIB increased both the activity of ornithine decarboxylase and, to a modest extent, the insulinotropic action of L-arginine and L-ornithine. Likewise, after treatment with AIB in vivo, the activity of ornithine decarboxylase increased tenfold or more in kidney, liver, pancreas, parotid gland and islet homogenates. The secretory response to D-glucose was little affected in islets removed from AIB-treated rats, but the insulinotropic action of L-arginine and L-ornithine were slightly increased. These findings suggest that the de novo generation of polyamines only plays a restricted role in the secretory response of islet cells to L-arginine and L-ornithine.