Central cardiovascular effects of kappa agonists dynorphin-(1-13) and ethylketocyclazocine in the anaesthetized rat.

Opiate kappa agonists were administered into the cisterna magna of normotensive urethane-anaesthetized artificially ventilated rats: ethylketocyclazocine (78.7 nM) (EKC) and dynorphin-(1-13) (62.3 nM) produced significant and long-lasting decreases in both blood pressure and heart rate. High doses of naloxone (1 mg/kg i.v.) were required to partially antagonize these effects. The central cardiovascular effects of EKC and dynorphin-(1-13) were compared to those of fentanyl (3 nM), [D-Ala2,Met5]enkephalinamide (17 nM) and beta-endorphin (2.9 nM) which induced increases in blood pressure and heart rate. These results suggest that opposite central cardiovascular effects could be induced by activation of various opiate receptors.