Differential effects of prostacyclin and prostaglandin E1 on bronchoconstriction and thrombocytopenia during collagen and arachidonate infusions and anaphylactic shock in the guinea-pig

Abstract

The antagonism by prostacyclin (PGI2) and prostaglandin E1 (PGE1) of bronchoconstriction induced by serotonin (5HT), collagen, arachidonic acid (AA) and anaphylaxis, as well as of thrombocytopenia was studied in the guinea-pig. Under conditions where PGE1 prevented bronchoconstriction by 5HT, by collagen or by AA better than the accompanying thrombocytopenia, PGI2 was a selective antagonist of bronchoconstriction due to collagen, but failed to interfere with that due to 5HT or to AA. Collagen-induced bronchoconstriction in the guinea-pig is platelet-dependent, being inhibited by immune platelet depletion, whereas that due to AA is platelet-independent. PGI2 blocks bronchoconstriction by collagen, because it prevents the platelet activation, and fails to interfere with bronchoconstriction by AA, even though it reduces the accompanying thrombocytopenia, because the role of platelets is negligible. PGE1 and PGI2 failed to interfere with thrombocytopenia or with bronchoconstriction of anaphylactic shock, and were inactive even when the acute bronchial effect was suppressed by anti-histamine treatment. Anaphylactic thrombocytopenia is beyond the control of agents which stimulate the cyclic AMP system, and involves specific mechanism which are not stimulated in platelet-rich plasma.