Potentiation of antinociceptive action of morphine by prostaglandin E1 in albino rats.

1. Prostaglandin E1 (0.4 ml/kg, i.p.) significantly potentiated the antinociceptive action of morphine in albino rats. 2. This potentiation was significantly inhibited by pretreatment with reserpine, p-chlorophenylalanine or methysergide but not by alpha-methyl-p-tyrosine, phentolamine or propranolol. 3. The results suggest that the potentiation of morphine by prostaglandin E1 is mediated by serotonin, since it is inhibited by pharmacological agents known to reduce central turnover of serotonin receptors.