Abstract

5-Hydroxytryptamine is an important neurotransmitter and hormone/paracrine agent mediating various enteric functions. The precise physiological and pathophysiological role of nitric oxide in 5- hydroxytryptamine-induced diarrhea remains unclear. Evidence is accumulating on the importance of nitric oxide in 5-hydroxytryptamine-induced secretion, but its role in fluid accumulation and electrolyte transport in jejunum and colon is not well established. This study therefore investigated in vivo, the effect of a nitric oxide synthase inhibitor and a nitric oxide precursor on intestinal fluid and electrolyte secretion induced by 5-hydroxytryptamine. Subcutaneous administration of 5-hydroxytryptamine (2-8 mg/kg) produced a dose-related increase in the intestinal fluid and electrolyte secretion in jejunum and in colon of the anaesthetized rats. 5-Hydroxytryptamineinduced (6.0 mg/kg, s.c.) jejunal and colonic fluid and electrolyte accumulation was inhibited by No-nitro-L-arginine (10-40 mg/kg, i.p.).The inhibitory effect of No-nitro-L-arginine was reversed by L-arginine (600-1 500 mg /kg, i.p.) dose-dependently but not by D-arginine (900 mg/kg, i.p.).These results demonstrate that, 5- hydroxytryptamine-induced fluid and electrolyte secretion in the jejunum and colon may involve nitric oxide.