Effect of prolactin on tolerance and dependence to acute administration of morphine

The effect of exogenous prolactin on the development of acute tolerance to and dependence on morphine was studied. As described elsewhere, analgesia induced by prolactin was subject to tolerance. Pretreatment with prolactin enhanced the development of tolerance to analgesia induced by morphine while it effectively suppressed the withdrawal symptoms. These results indicate that prolactin behaves like an opioid agonist and suggest that it may have therapeutic implications in the management of opioid dependence.