Prolactin release in lactating, primiparous and multiparous thelectomized and maternal virgin rats exposed to pup stimuli.

Abstract

Serum prolactin was measured by radioimmunoassay in primiparous lactating (L), primiparous thelectomized (nipple removed; PT), multiparous thelectomized (with 1 prior normal lactation experience; MT), virgins (MV) induced to display maternal behavior (retrieving, pup licking and adopting the lactating position) and in nonmaternal virgin females (NMV) not previously exposed to pups. On postpartum Day 7 or on 1 diestrous day between Days 6–10 after the onset of maternal care in the MV group, pups were removed at 0900 h and were either returned or not returned at 1500 h. Rats were decapitated at 1530 h. Prolactin was significantly higher when pups were returned to the L and MT groups and the MV group that had been maternal for 8–10 days and, among these groups, prolactin levels were: L>MT = MV (Days 8–10). Thus, prolactin is released in response to pup stimuli in the absence of suckling and is influenced by a previous lactation experience and by the concurrent duration of the maternal behavior state in virgin rats.