Evidence of direct positive inotropic and chronotropic actions by PGE1 not mediated by cyclic AMP in conscious sheep.
The underlying mechanism for the cardiac responses to PGE1 has not yet been fully elucidated. In order to investigate a possible role for cyclic AMP in the positive inotropic and chronotropic actions of prostaglandin E1 (PGE1) in conscious sheep, theophylline-ethylenediamine was used to inhibit phosphodiesterase activity. Any significant potentiation or the lack of potentiation of the measured cardiac response to PGE1 was then used as a criterion to establish whether the cardiac actions of PGE1 were produced by an alteration in the intracellular levels of cyclic AMP. The results suggest that PGE1 produced positive inotropic and chronotropic actions in conscious sheep, which is neither caused by the autonomic nervous system (baroreflexes) nor by changes in intracellular cyclic AMP levels. Further research seems warranted to establish whether a relationship exists between Ca2+ and the contractile response of PGE1. Such a relationship could then possibly explain the positive inotropic action of PGE1 in conscious sheep.
Schutte
P J
PJ
Department of Physiology, Medical University of Southern Africa, Medunsa.
du Plooy
W J
WJ
van Reenen
O R
OR
D000818:Animals; D000242:Cyclic AMP / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011458:Prostaglandins E / Q000494:pharmacology*; D012756:Sheep
D010726:Phosphodiesterase Inhibitors; D011458:Prostaglandins E; D000242:Cyclic AMP