Effect of dihomo-gamma-linolenic acid on the canine pulmonary vascular bed

The effect of dihomo-gamma-linolenic acid (DGLA), the precursor of the monoenoic prostaglandins (PG), F1alpha and E1, on the pulmonary vascular bed of the intact dog was studied under conditions of controlled pulmonary blood flow. DGLA increased pulmonary vascular resistance in a dose-related manner by constricting intrapulmonary veins and upstream segments, presumably pulmonary arteries. Intrapulmonary injection of DGLA also increased transpulmonary injection of DGLA also increased transpulmonary airway pressure, presumably by increasing airway resistance and decreasing lung compliance or both. The vasoconstrictor response, however, was independent of changes in transpulmonary pressure since similar pressor responses were obtained in ventilated and nonventilated lungs. Further, the response was not dependent on factors or elements in whole blood, since the increase in pulmonary vascular resistance occurred during perfusion with saline or dextran and was enhanced in these media. Conversion of DGLA to PGs by a lung cyclo-oxygenase appears to mediate the response, since it was blocked by indomethacin and dose not occur with injection of nonprecursor long-chain fatty acids. These data suggest that the response to DGLA is due to formation of vasoactive products in the monoenoic PG pathway.