Effects of inhibiting nitric oxide biosynthesis on the systemic and splanchnic circulation of rats with portal hypertension

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Abstract
1 The effects of inhibiting endogenous nitric oxide (NO) synthesis with NG-monomethyl-l-arginine (l-NMMA) on the systemic and splanchnic circulation have been investigated in rats with experimental chronic portal hypertension, anaesthetized with ketamine. 2 Portal hypertension was induced by partial portal vein ligation, 2 weeks prior to study. This procedure induced a reduction in systemic arterial blood pressure (MAP), an increase in cardiac output as measured by radiolabelled microspheres, a reduction in peripheral and splanchnic vascular resistance and an increased portal venous inflow (PVI) and portal pressure, as compared to control non-ligated rats. 3 l-NMAA (6.25 and 50 mg kg−1, i.v.) dose-dependently increased MAP, reduced cardiac output and PVI, and increased peripheral and splanchnic vascular resistance. With l-NMMA (50 mg kg−1), PVI and the vascular resistances returned to values comparable to those determined in control non-ligated anaesthetized rats under resting conditions. 4 Porto-collateral resistance was also increased by these doses of l-NMMA, whereas portal pressure was unchanged. The increase in renal blood flow and decrease in renal vascular resistance also seen in portal-hypertensive rats was reversed by l-NMMA (50 mg kg−1). 5 These effects of l-NMMA (50 mg kg−1) were inhibited by prior administration of l-arginine (300 mg kg−1, i.v.). 6 These findings indicate that the chronic hyperdynamic circulatory characteristics following portal vein stenosis can be attenuated by l-NMMA. Thus, the excessive formation of endogenous NO may be implicated in the pathogenesis of the haemodynamic disturbances and splanchnic vasodilatation associated with chronic portal hypertension.