Possible opioid participation in the analgesic effects of the renin-angiotensin system.

Using the tail-flick method in 45 rats with a chronic cannula stereotaxically implanted in the third ventricle, a rapid onset, dose related and short lasting analgesia was obtained after intracerebroventricular injection of Ang II 10-15 ng/kg or renin 0.03-0.1 U. Analgesic effects of the endogenous and exogenous Ang II are prevented by naloxone--1 mg/kg i.p. The inhibition of serotonin synthesis with PCPA--400 mg/kg/day i.p. for five days as well as the serotonin-receptor block with ketanserin 0.1 mg/kg i.p. partially prevent analgesic effects of Ang II and renin intracerebral administration. The increase of the pain perception threshold after infusing into the brain Ang II or renin points out a new functional consequence of the possible opioid participation in the central effects of renin-angiotensin system.