Naloxone potentiates the inotropic effects of isoproterenol in vitro by a nonopiate receptor mechanism
Lechner, R.B.
Circulatory Shock 38(3): 157-164
1992
ISSN/ISBN: 0092-6213 PMID: 1338035 Document Number: 393696
Naloxone potentiates the effects of adrenergic agonists when administered to hypovolemic dogs, and it has been assumed that this effect is due to naloxone's action at opiate receptors. To help determine the site and mechanism of this interaction, we administered naloxone and its "d" stereo-isomer (which does not bind to opiate receptors) to guinea pig papillary muscles in the presence and absence of pharmacologic (isoproterenol) and physiologic (treppe) inotropic stimulation. In control muscles and in rapidly paced muscles, naloxone was without significant inotropic effect. In the presence of isoproterenol, d- and l-naloxone exerted significant positive inotropic effects that were dose dependent. We conclude that, since both d- and l-naloxone potentiated the inotropic effects of isoproterenol and this was seen in the absence of opioids, naloxone may increase contractility by a nonopiate receptor-mediated mechanism.