RESPONSES OF PULMONARY AND SYSTEMIC CIRCULATIONS OF PERINATAL GOATS TO PROSTAGLANDIN F-2ALPHA

The effects of exogenous prostaglandin (PG) F2(α) and the 15-keto metabolites of both prostaglandins, upon unventilated fetal, premature newborn, and mature newborn goat pulmonary and systemic circulations were examined by infusing the compounds into the pulmonary circulation. PGF2(α) is a powerful pressor agent in both pulmonary and systemic circulations of fetal and neonatal goats. Broncho-pulmonary constriction was also observed in ventilated animals at infusion rates in excess of the lung's ability to catabolize the prostaglandin. The pressor effects were not attenuated by alpha-adrenergic blockade. PGF1(α) is qualitatively similar, but quantitatively less, in its effect. The 15-keto metabolites did not alter pulmonary or systemic circulation even at very high doses. The PGF2(α) threshold dose for increasing pulmonary vascular resistance is lowest in the unventilated fetus, greatest in the premature newborn, and intermediate in the newborn older than 1 day of age. The lower sensitivity of the pulmonary circulation to the exogenous vasoconstrictor in the immediate postventilation period suggests the presence of endogenous dilator activity. Since the increase in pulmonary vascular resistance produced by indomethacin is greatest in the newly ventilated fetus, less in the older newborn, and negligible in the unventilated fetus, the substance(s) responsible for the endogenous dilator activity would appear to require prostaglandin fatty acid cyclooxygenase activity for production.