ESTRADIOL, PROGESTERONE, AND PROLACTIN REGULATE MATERNAL NEST-BUILDING IN RABBITS

Maternal nest-building in rabbits, expressed across the last third of pregnancy, consists of: digging a burrow, collecting straw and shaping it into a nest inside the burrow, plucking body hair and lining the s traw nest with it, The sequential expression of these activities is co rrelated with specific changes in the plasma concentration of estradio l, progesterone (P), and prolactin (PRL), To further substantiate the participation of these hormones in the control of maternal nest-buildi ng we explored in ovariectomized (ovx) New Zealand white rabbits the c apacity of several combinations of such hormones to stimulate digging, straw-carrying, and hair-pulling, Does given estradiol benzoate (EB; 5 mu g/day from days 3 to 21) plus P (2 or 10 mg/day from days 4 to 16 ) dug into a substrate from the fourth day of the P treatment until wi thdrawal of this hormone. The intensity of this effect was greater in the group treated with the high dose of P, Straw-carrying and hair-pul ling occurred after P withdrawal in a dose-response way, Food intake, which declines in pregnant females shortly before parturition, decreas ed to the same extent in both groups of ovx EB-treated does after P wi thdrawal, A significant increase in PRL plasma levels was observed on day 9 in does given EB plus 2 mg P/day and at two days following P wit hdrawal in does given EB plus 10 mg P/day, When such ovx EB/P-treated does were given bromocriptine to block PRL release (1 or 3 mg/Kg/day, from days 11 to 21) the expression of digging was unmodified, By contr ast, bromocriptine abolished the display of straw-carrying and hair-pu lling, and also prevented the decline in food intake normally followin g P withdrawal. The addition of ovine PRL to ovx EB/P-treated does giv en bromocriptine reduced the expression of digging, did not restore st raw-carrying or hair-pulling, and provoked a sharp decline in food int ake. The possible mechanisms of interaction between PRL and steroid ho rmones for the regulation of specific aspects of the pregnant doe's ph ysiology and behavior are discussed.