IN PIGS, INHALED NITRIC-OXIDE (NO) COUNTERBALANCES PAF-INDUCED PULMONARY-HYPERTENSION

In 6 anesthetized mechanically ventilated pigs we have studied the eff ects of inhalation of 80 ppm of nitric oxide (NO) before and after pla telet-activating factor (PAF) administration (50 ng/kg iv). Our result s show that NO inhalation causes a decrease in pulmonary arterial pres sure and in heart rate without affecting other circulatory parameters. PAF administration causes a pulmonary hypertension and a prompt and b rief decrease in systemic pressure. Inhalation of NO reduces the pulmo nary hypertension, without completely reversing PAF-dependent vasocons triction. PAF administration to pigs pretreated with indomethacin prod uces a lesser increase in pulmonary vascular pressure. In this case, N O inhalation can restore to baseline values. Pretreatment of 3 of the 6 pigs with N-G-nitro-L-arginine-methyl-ester did not prevent the prom pt and brief PAF-induced systemic hypotension. In conclusion, our resu lts show that NO reduces basal pulmonary vascular tone, acts as a pulm onary vasodilator on PAF-preconstricted vessels and is not involved in the brief systemic hypotension consequent to PAF administration.