ACUTE HYPOTENSION ALTERS HEMODYNAMIC-RESPONSE TO METHIONINE-ENKEPHALIN IN CONSCIOUS DOGS

In the conscious dog, intravenous administration of methionine-produce s simultaneous increases in both heart rate (HR) and mean arterial blo od pressure (MAP). This report describes both depressor and cardioacce lerator responses to methionine-enkephalin (10 mug/kg IV) in conscious dogs following acute hypotension induoed by either bolus injection of isoproterenol (0.1-5.0 mug/kg IV) or infusion of sodium nitroprusside (SNP, 3-8 mu/kg/min). Cardiovascular responses to methionine-enkephal in were blocked by naloxone. Pretreatment of the dogs with the beta-ad renergic receptor antagonist propranolol failed to prevent the hypoten sive response to methionine-enkephalin following SNP infusion. The res ults indicate that the hemodynamic responses to methionine-enkephalin can be altered by acute manipulation of blood pressure. These results may have implications relative to the role of endogenous opiates in re gulation of blood pressure, especially in acute hypotensive states.