Bovine adrenal medulla 22 reverses antinociceptive morphine tolerance in the rat

Acute intrathecal (i.t.) bovine adrenal medulla 22 (BAM22, 10 nmol), an endogenous opioid peptide, induced equipotent thermal antinociception in naïve and morphine-tolerant rats while chronic BAM22 resulted in hyperalgesia and decrease in the effectiveness of antinociception. In rats made tolerant to morphine, prior administration of BAM22 (10 nmol, i.t.) significantly resumed antinociceptive response of morphine. The present study demonstrated that BAM22 was able to modulate maintenance of morphine tolerance.