Evidence for a role of endorphins in stress- and suckling-induced prolactin release in the rat.

Injection of the opiate antagonist naloxone completely prevented the rise of serum prolactin induced by ether stress in intact male rats. Naloxone also led to a 50--95% inhibition of the marked elevation of plasma prolactin levels induced by suckling. These data suggest that endogenous opiates (endorphins) are involved in the stimulation of prolactin release induced by both stress and suckling in the rat.