PGI(2) AND NITRIC-OXIDE INVOLVEMENT IN THE REGULATION OF SYSTEM AND PULMONARY BASAL VASCULAR TONE IN THE PIG

In anesthetized, ventilated pigs we analyzed the involvement of nitric oxide (NO) and prostaglandins (PGs) in the regulation of systemic and pulmonary basal vascular tone. Endogenous release of NO was blocked b y N-G-nitro-L-arginine methyl ester (L-NAME) and prostanoid biosynthes is by indomethacin. Blocking NO raised pulmonary and systemic arterial pressure and vascular resistances. These effects show that in the pig there is continuous release of minute amounts of NO. Blocking prostan oid biosynthesis did not affect the vasoconstrictor effect of L-NAME o n the pulmonary vascular bed, but significantly strengthened the hyper tensive effect of L-NAME on the systemic vascular bed. These data show that different mechanisms regulate pulmonary and systemic vascular to ne, Administration of a stable analogue of PGI, to pigs pretreated wit h indomethacin reversed the systemic vasoconstrictor effect of L-NAME, In conclusion, our data show that NO especially modulates pulmonary v ascular tone, while PGI, preferentially modulates systemic vascular to ne.