Enalapril, a new nonsulfhydryl angiotensin converting enzyme inhibitor, does not potentiate morphine analgesia.

Sprague-Dawley rats received oral doses of enalapril maleate (5 mg/kg), a potent, nonsulfhydryl, angiotensin converting enzyme inhibitor, or saline. Sixty min later, morphine sulfate, 5 mg/kg, or saline was injected subcutaneously. Response to a thermal stimulus was monitored before and up to 5 h ter morphine injection using the rat tail flick test. Serum ACE activity was greater than 90% inhibited by enalapril throughout the experiment. Enalapril did not exhibit analgesic activity nor did it potentiate morphine analgesia.