Cardiovascular effects of morphine and opioid peptides following intracisternal administration in chloralose-anesthetized rats.

Beta-Endorphin (0.9--2.0 nmol), morphine (11--250 nmol) and D-ala2-met-enkephalinamide (17--33 nmol) administered intracisternally produced preferential vasodepressor responses and bradycardia. Leu- (1.8--180 nmol), met-enkephalin (17--520 nmol) and alpha-endorphin (5.7--57 nmol) administered in the same way produced preferential vasopressor effects and the latter two peptides also produced bradycardia. Results obtained with naloxone (300 nmol) given intracisternally indicate that the pressor and depressor actions as well as the bradycardia are mediated through opiate receptors. The results indicate that opioid peptides may be involved in central cardiovascular control.