Reversal of 5HT-induced bronchoconstriction by PGI2: distribution of central and peripheral actions

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Abstract
In anesthetized, mechanically ventilated, and vagotomized cats, we studied the distribution of the bronchodilatory effects of prostaglandin I2 (PGI2) in central and peripheral airways. In the intact-chest cat, bolus intravenous injection of PGI2 in a range of doses from 3 to 100 micrograms produced dose-dependent reversal of 5-hydroxytryptamine- (5HT) induced bronchoconstriction. Bronchodilatory effects were manifested by a pronounced decrease in central airways flow resistance, as estimated by measurement of lung resistance and by an increase in dynamic lung compliance (Cdyn). A similar distribution and magnitude of airway effects were produced by intravenous administration of PGE1 in a range of doses from 0.3 to 10 micrograms. PGI2 significantly reversed the frequency dependence of compliance induced by infusion of 5HT. The PGI2 metabolite, 6-keto-PGF1 alpha, was without effect on pulmonary mechanics. Comparison of right- versus left-heart administration of PGI2 did not point to a significant role of the bronchial circulation in the airway effects of PGI2. Comparison of the effects of PGI2 and PGE1 on cat bronchial and parenchymal strips contracted by 5HT showed both prostaglandins to have predominant action on bronchial smooth muscle with PGI2 being 3-10 times less active than PGE1. These data suggest that PGI2 has central airway bronchodilator activity, similar to, but less potent than PGE1. In addition, they suggest that PGI2 has significant dilator activity in certain peripheral areas of the lung, as well.