Analgesic effect of prolactin: possible mechanism of action

The analgesic effect of prolactin (PRL) was tested by means of the acetic acid-induced writhing test and the hot plate method. In both assays PRL produced dose-dependent analgesia. This was antagonised by naltrexone indicating the involvement of opiate mechanisms. Bromocriptine, which inhibits PRL secretion through dopaminergic activity, also antagonised PRL-induced analgesia implicating dopaminergic mechanisms in this action of PRL. It is suggested that pituitary peptides may have a role in pain modulation along with the endogenous opioid peptides.