Endogenous nitric oxide attenuates ethanol‐induced perturbation of hepatic circulation in the isolated perfused rat liver

The purpose of this study was to clarify the role of endogenous nitric oxide in ethanol‐induced perturbation of microcirculation and hepatic injury in perfused rat liver. Infusion of ethanol into the portal vein at 25 and 100 mmol/L increased portal pressure, which is an indicator of hepatic vasoconstriction, in a concentration‐dependent fashion. Portal pressure started to rise immediately after ethanol load, then decreased gradually and remained at higher than basal levels throughout the period of ethanol infusion. Release of lactate dehydrogenase into the effluent perfusate began to increase after 30 min of ethanol infusion and continued to increase during the 60‐min period of ethanol infusion. The lactate dehydrogenase level in the effluent perfusate at 60 min was dependent on the ethanol concentration (0 mmol/, 8 ± 3 IU/L 25 mmol/L, 16 ± 2 IU/L 100 mmol/L, 52 ± 6 IU/L). Simultaneous infusion of NG‐monomethyl‐L‐arginine, a nitric oxide synthesis inhibitor, enhanced significantly the ethanol‐induced increase in portal pressure by 100% to 400% and increased lactate dehydrogenase release by 40% to 80%. The effect of NG‐monomethyl‐L‐arginine on the ethanol‐induced increase in portal pressure was completely reversed by the co‐infusion of an excess dose of L‐arginine. Change in portal pressure averaged over 60 min of ethanol infusion correlated with levels of lactate dehydrogenase release 60 min after the initiation of ethanol infusion (r = 0.77, p < 0.01). In conclusion, inhibition of the action of endogenous nitric oxide was associated with an increase in hepatic vasoconstriction and hepatocellular damage. These results suggest that endogenous nitric oxide acts as a vasodilator that reduces ethanol‐induced vasoconstriction, thus improving microcirculation and leading to decreased hepatic damage. (Hepatology 1994;20:961–965).