Release of prostaglandin-like substances and lung reactions to induced intravascular platelet aggregation in cats

Abstract

Induced intravascular aggregation of blood platelets gives pulmonary vasoconstrictor and bronchoconstrictor responses, which might be mediated by bioactive substances from the platelets. The aim of the present work was to see if these lung reactions could be related to the release of prostaglandin-like substances (PGLS). Repeated episodes of platelet aggregation were induced by i.v. infusions of collagen in anaesthetized cats ventilated at a constant tidal volume. Arterial blood was pumped from a carotid artery (10 ml/min) to super-fuse a series of smooth muscle organs sensitive to prostaglandins (PGs): rabbit aorta, rat stomach strip, rat colon and chick rectum. In two experiments cat jejunum replaced the rabbit aorta in order to detect kinins. All tissues were pre-treated with antagonists against catecholamines, histamine, serotonin and acetylcholine. The bioassay tissues were calibrated with standard doses of PGE₂ and PGF_2α, Collagen infusions caused lung responses (as judged from the rise in peak tracheal pressure) and in most cases also a transient systemic hypotension. Simultaneously, contractions of the bioassay tissues occurred, indicating release of PGLS. Such release was only detected as long as lung responses could be elicited by i.v. collagen infusions. These findings imply that PGs and/or the various intermediates in PG synthesis might mediate the pulmonary smooth muscle constriction occurring after intravascular platelet aggregation.