Pulmonary vasodilator activity of prostacyclin (PGI2) in the cat

We studied the pulmonary vascular effects of prostacylin, PGI2, in the cat with intact chest under conditions of controlled blood flow. Intralobar injections of PGI2, 0.03--1 microgram, decreased arterial pressure in the perfused lobe in a dose-dependent manner. Inasmuch as lobar blood flow was held constant and left artrial pressure was unchanged, the fall in lobar arterial pressure reflects a decrease in lobar vascular resistance. Prostaglandin E1 (PGE1) and nitroglycerin also decreased lobar arterial pressure; however, PGI2 had greater vasodilator activity than did these substances. Vasodilator responses to PGI2, PGE1, and nitroglycerin in absolute terms were dependent on the baseline level of tone in the pulmonary vascular bed. Prostacyclin reversed the hypertensive and platelet aggregating effects of ADP in the lobar vascular bed. These data indicate that PGI2 has significant vasodilator activity in the feline pulmonary lobar vascular bed.