EFFECTS OF INHALED NITRIC-OXIDE IN RATS WITH CHEMICALLY-INDUCED PULMONARY-HYPERTENSION

To determine the model animal with pulmonary hypertension in which nit ric oxide (NO) inhalation reduces pulmonary arterial pressure (PAP), w e examined the inhalation of 20-100 ppm NO gas on normal rats and rats with monocrotaline induced pulmonary hypertension. In the control gro up, mean PAP showed no change after spontaneous breathing of NO at the concentration of 20 to 100 ppm for 5 min. On the contrary, in both th e severe (mean PAP>40 mmHg) and moderate (mean PAP<40 mmHg) pulmonary hypertensive groups, NO inhalation produced a prompt reduction of the mean PAP which had been elevated by monocrotaline. 20 ppm NO inhalatio n reduced mean PAP from 64.4 +/- 3.7 mmHg to 56.2 +/- 4.4 mmHg (mean /- SEM, P<0.01) in the severe pulmonary hypertensive group, from 31.0 +/- 2.0 mmHg to 24.2 +/- 0.9 mmHg in the moderate pulmonary hypertensi ve group (mean +/- SEM, P<0.05). The onset of the reduction of mean PA P occurred within 30 sec after the start of NO inhalation and maximum reduction occurred within 4 min. 20 ppm NO inhalation significantly re duced mean PAP, and mean PAP was reduced dose-dependently at the conce ntration of 20 to 60 ppm and reaction to NO was almost constant at the concentrations of over 60 ppm.