Pulmonary and systemic vasodilator effects of the newly discovered prostaglandin, PGI2

The effects of the newly discovered bicyclic prostaglandin, prostacyclin (PGI2), on the pulmonary and systemic vascular beds were investigated in the anesthetized dog. PGI2 decreased systemic and pulmonary arterial pressures in a dose-related manner when injected into the vena cava in doses of 1--30 microgram. Since left ventricular end-diastolic, left atrial, and right atrial pressures were unchanged, and since cardiac output was increased or unchanged, pulmonary and systemic vascular resistances were decreased. PGI2 was 10 times more potent than prostaglandins E1 or E2 in decreasing aortic pressure when injected intravenously, and the effects of PGI2 on the systemic vascular bed were similar when injected into the vena cava or the left atrium. These data indicate that inactivation of PGI2 is minimal in the lung. The stable prostacyclin metabolite, 6-keto-PGF1alpha, had little hemodynamic effects, suggesting that responses to PGI2 were not due to formation of this metabolite. PGI2 produced dose-dependent increases in blood flow in the mesenteric and renal vascular beds. These data demonstrate that PGI2 has marked vasodilator activity in the pulmonary and systemic vascular beds and suggest that prostacyclin is the only known metabolite of arachidonic acid that dilates the pulmonary and systemic circulations.