Microcirculatory and motor effects of endogenous nitric oxide in the rat gut

The aim of the study was to determine the role of endogenous nitric oxide (NO) as the mediator of intestinal blood flow and motility. Experiments were performed on anesthetized rats. Blood flow in the jejunum was determined by Laser-Doppler flowmeter. Motility was monitored on the basis of changes in intrajejunal pressure. Systemic arterial pressure was also recorded. To investigate the potential role of nitric oxide in the regulation of basal intestinal blood flow and motility the NO synthase inhibitor NG-nitro-L-arginine (L-NNA) was given systemically. Intravenous bolus of L-NNA (15 mg/kg) reduced basal intestinal blood flow and increased both intestinal motility and arterial pressure in the dose-dependent manner. To test the specificity of the NO synthase blockade we administered L-arginine alone or in combination with L-NNA. Pretreatment with L-arginine (100.0 mg/kg i.v.) alone had no major influence but when combined with L-NNA it reversed the intestinal circulatory and motor effects of L-NNA. The results of these studies suggest that endogenous NO exerts a tonic relaxatory influence on the smooth muscle of the intestinal vessels and intestinal wall.