Effects of ergocryptine on prolactin secretion druing concurrent pregnancy and lactation in the rat.

Ergocryptine (2 mg/kg) caused short- and long-term reduction of prolactin secretion in rats experiencing concurrent lactation and pregnancy. The long-term effects of the drug lasted at least 60 days and resulted in reduced milk secretion and termination of pregnancy. Prolactin replacement therapy at a low dose (5 i.u./day) was unsuccessful in overcoming these effects but a higher dose (up to 60 i.u./day) increased milk production and maintained pregnancy. One possible explanation of these results is that prolactin, rather than the suckling stimulus, was responsible for the suppression of oestrous cycles, because ergocryptine brought about a resumption of oestrous vaginal smears in all treated rats in spite of continued suckling.