Blood pressure and cardiac tissue responses to prostacyclin (PGI2) in various species

Abstract

Prostacyclin (PGI2) is a powerful inhibitor of platelet aggregation with vasodilator and vasodepressor actions. The effect of PGI2 on blood pressure and heart rate (in vivo) and on isolated heart tissue was investigated in different species. Isolated cardiac tissue had limited responses to PGI2 tested at 10-13 to 10-5 M. Cultured neonatal rat heart cells did not respond to PGI2, neither did intact rat hearts or rabbit cardiac tissue. Guinea pig and rat atria showed limited dose-dependent responses to PGI2 at concentrations > 10-7 M. In rat atria, 10-5 M PGI2 produced a limited elevation of tissue cAMP content. When given by i.v. injection or infusion, PGI2 produced hypotension in anesthetized primates (3 spp.), rat, rabbit, pig and dog. As a vasodepressor in all species, PGI2 (on a weight basis) was more active than prostaglandins [PG] of the B or E type and, in most species tested, it was .apprx. 5 times more active than PGE2. Heart responses in intact animals were often paradoxical in that decreases in heart rate often accompanied blood pressure falls.