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 vas cular hyporeactivity in portal vein-ligated rats was assessed in isola ted perfused mesenteric arterial beds. Aminoguanidine, a selective inh ibitor of the inducible NO synthase, restored the presser responses to methoxamine in arteries of endotoxin-treated rats, but was ineffectiv e in hyporeactive portal vein-ligated vessels. N-G-Nitro-L-arginine me thyl ester enhanced the responsiveness both in portal vein-ligated and sham-operated rats, without changing the difference between the two g roups. These results not only indicate that the inducible NO synthase is not involved in the hyporeactivity to methoxamine in mesenteric art eries of portal hypertensive rats, but also suggest a role for factors other than NO.