Nitric oxide is involved in the insulin release in rats by l-arginine

Abstract

The insulinogenic effect of l-arginine has been demonstrated both in vivo and in vitro, but the mechanism by which this amino acid stimulates the pancreatic B-cells to release insulin is not entirely clear. Recently it was shown that l-arginine-derived nitric oxide may mediate l-arginine-induced insulin release, and data were also provided to suggest that nitric oxide (NO) has no part in this process. To further investigate whether NO is involved in the release of insulin induced by l-arginine, we infused different doses of l- and d-arginine in rats. L-Arginine (25 and 100 mg/kg/minute) elicited dose-dependent increases of the plasma insulin levels by up to 18.65 ± 2.13 and 48.6 ± 6.6 U/L, respectively, and increased the plasma glucose levels by up to 1.18 ± 0.13 and 1.43 ± 0.1 mmol/L, respectively. D-Arginine (25 and 100 mg/kg/minute) also elicited dose-dependent increases of the plasma insulin levels by up to 9.08 ± 1.23 and 23.33 ± 2.33 U/L, and increased the plasma glucose levels by up to 0.32 ± 0.09 and 0.46 ± 0.08 mmol/L. Thus, the increases in plasma insulin and glucose levels were significantly smaller during infusion of d-arginine. We conclude that the plasma insulin response to i.v. infusion of l-arginine is at least partly mediated by augmented NO synthesis by the pancreatic islets, although l-arginine-derived NO is not an obligatory stimulus for insulin release.