Release of prostaglandin-like substances during elevations of left atrial pressure in the cat

The purpose of the present work was to measure prostaglandin (PG)-like activity in arterial blood during acute pulmonary hypertension. Anesthetized cats with the chest opened and given positive pressure ventilation were used. A balloon in the left atrium was inflated to elevate hydrostatic vascular pressure in the lungs. Blood was pumped (10 ml/min) from a carotid artery to superfuse 3 smooth muscle tissues: rat stomach strip, rat colon and chick rectum: the blood was then returned to the jugular vein by gravity. The assay tissues were pretreated with antagonists against catecholamines, histamine, serotonin and acetylcholine during the experiments. They were sensitive to calibrating doses of 2 ng/ml of PGF2 alpha and 1 ng/ml of PGE2. 18 periods with elevated left atrial pressure (P LA) (21--49 mmHg), lasting 2--26 min, were applied in 9 cats. This manoevre usually also caused systemic hypotension. 14 of these PLA elevations were accompanied by increased arterial PG-like activity, which rapidly subsided when the pressure was released or when indomethacin (2 mg/kg, n = 4) was given i.v. In 3 additional experiments it was found that pulmonary degradation of PGs was unaffected during P LA elevation. I.v. infusion of angiotensin II contracted the tissues in a pattern different from that caused by pressure elevations and the PG calibrations, and these contractions were not affected by indomethacin. This indicates that the assay tissue contractions cannot be caused by angiotensin II which alone does not increase PG-like activity in arterial blood. Consequently, acute pulmonary vascular hypertension appears to stimulate PG synthesis and release in lungs of intact cats.