THE ROLE OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN VASCULAR HYPOREACTIVITY OF ENDOTOXIN-TREATED AND PORTAL HYPERTENSIVE RATS

The involvement of the inducible nitric oxide (NO) synthase in the vascular hyporeactivity in portal vein-ligated rats was assessed in isolated perfused mesenteric arterial beds. Aminoguanidine, a selective inhibitor of the inducible NO synthase, restored the presser responses to methoxamine in arteries of endotoxin-treated rats, but was ineffective in hyporeactive portal vein-ligated vessels. N-G-Nitro-L-arginine methyl ester enhanced the responsiveness both in portal vein-ligated and sham-operated rats, without changing the difference between the two groups. These results not only indicate that the inducible NO synthase is not involved in the hyporeactivity to methoxamine in mesenteric arteries of portal hypertensive rats, but also suggest a role for factors other than NO.