Effects of brain natriuretic peptide on effects of morphine in mice

Brain natriuretic peptide (BNP) is a member of the natriuretic peptide family. The effects of intracerebroventricularly administered BNP (in 0.002–200 ng doses) on the analgesic, tolerance-inducing and dependence-inducing actions of morphine were investigated in adult male CFLP mice. Graded doses of BNP centrally did not affect pain sensitivity itself in a tail-flick test. However, different doses of BNP depressed the acute nociceptive effect of a single subcutaneous dose of morphine (5 mg/kg), and BNP attenuated the development of acute and chronic tolerance to morphine. Withdrawal signs were studied by injecting naloxone (1 mg/kg s.c.). There was no significant difference in symptoms between the tolerant group and animals treated with BNP. The data obtained indicate that BNP can modify the analgesic action of morphine.