Buprenorphine: bell-shaped dose-response curve for its antagonist effects.

1. Doses of buprenorphine (0.01, 0.1, 0.5, 1, 5, 10 and 50 mg/kg) were administered to determine buprenorphine's ability to precipitate abstinence symptoms in morphine-dependent mice. 2. When buprenorphine was administered in the fourth day of morphine addiction, the results demonstrate that the administration of the partial agonist opioid produce a bell-shaped dose-response curve. 3. The highest dose (50 mg/kg) was partially inactive while lower doses causing similar percentage than group treated with naloxone with respect to the appearance of the most of the symptoms of abstinence studied (diarrhoea, tremor, shaking-"wet dog shakes"-, jumping and weight loss). 4. Our findings demonstrate the bell-shaped response curve of the antagonist effects of buprenorphine.