Role of pup age, estradiol-17 beta and pituitary responsiveness in the differences in the suckling-induced prolactin response during early and late lactation.
The suckling-induced prolactin (Prl) response was studied in 10- and 20-day postpartum female rats. The response in 20-day postpartum mothers has a slower onset, has markedly reduced peak values and returns to baseline somewhat sooner than the response in 10-day postpartum mothers. The blunted response of late lactation was seen in mothers suckled for 30 min and was maintained over a longer interval in mothers continuously suckled for 120 min. This refractory phenomenon was not due to decreased suckling intensity provided by 20-day relative to 10-day-old pups. Pituitary gland Prl release in response to thyrotropin releasing hormone (TRH) and haloperidol challenges also did not distinguish 10- from 20-day postpartum mothers. Significantly higher estradiol-17 beta levels were found in 20-day compared with 10-day postpartum mothers, a finding which cannot account for the blunted response. Pup separation from 10-day postpartum mothers for 4, 24, 48 or 72 h did not produce a blunted response like that seen in late lactation. It is suggested that the hypothalamic mechanism mediating suckling-induced Prl release becomes refractory to the suckling stimulus during the preweaning period.
D000818:Animals; D004958:Estradiol / Q000502:physiology*; D005260:Female; D006220:Haloperidol / Q000494:pharmacology; D007774:Lactation; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D011247:Pregnancy; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D004958:Estradiol; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D006220:Haloperidol