Cardiovascular effects of intrathecally injected mu, delta and kappa opioid receptor agonists in rabbits.

1. Intrathecal saline, the mu opioid agonist [D-Ala2, MePhe4, Gly5-ol] enkephalin (DAGO) and delta opioid agonist [D-Pen2, D-Pen5] enkephalin (DPDPE) had no significant effects on systemic blood pressure and heart rate values. 2. The kappa opioid agonist bremazocine however, caused falls in blood pressure and reduction in heart rate. 3. Intrathecal administration of saline, DPDPE and bremazocine had no effect on baroreflex sensitivity. 4. Intrathecal administration of DAGO caused a reduction in baroreflex sensitivity; this effect was inhibited by naloxone and abolished after atenolol. 5. The role of spinal opioid systems as a possible site of action is discussed.