Lactogenic hormones of the placenta and pituitary inhibit suckling-induced prolactin (PRL) release but not the ante-partum PRL surge.

Abstract

Prolactin (PRL) and other lactogenic hormones feed back at the hypothalamus to inhibit PRL release. At midpregnancy, high circulating levels of placental lactogens (PL) terminate the mating-induced biphasic PRL surges in female rats. In the dark period preceding parturition, however, an ante-partum PRL surge occurs despite continuously high levels of PL. This study examined whether the lactogenic hormone negative feedback loop is altered during the ante-partum surge using two models: (i) pregnant rats given a hypothalamic implant of albumin, ovine PRL, or recombinant rat PL-I on Day 19 or 20 of pregnancy; and (ii) pregnant rats bearing a transplant of a rat choriocarcinoma cell line, Rcho-1 (PL-secreting), or HRP-1 (non-PL-secreting). Serial blood samples were taken via carotid cannula from all rats. Although lactogenic hormones placed in the hypothalamus reduced suckling-induced PRL release by 89%, hypothalamic implants of oPRL or recombinant rPL-I did not attenuate the ante-partum PRL surge. Rcho-transplanted rats also did not have a significantly reduced ante-partum PRL surge (peak PRL level, 131 ng/ml) compared with HRP-bearing rats (peak PRL level, 107 ng/ml). Northern blot analysis revealed that the Rcho-1 tumors expressed both PL-I and PL-II, while the HRP-1 tumors did not express either PL. The inability of the Rcho-1 transplants to inhibit the ante-partum PRL surge suggests that lactogenic hormone negative feedback is disrupted during the ante-partum period, possibly by the changing steroid profile associated with parturition.

• Authors: R J Fliestra, J L Voogt
• Journal: Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.) (Proc Soc Exp Biol Med) Vol. 214 Issue 3 Pg. 258-64 (Mar 1997) ISSN: 0037-9727 [Print] United States
• PMID: 9083259 (Publication Type: Journal Article, Research Support, U.S. Gov't, Non-P.H.S., Research Support, U.S. Gov't, P.H.S.)

Chemical References

• RNA, Messenger
• RNA, Neoplasm
• placental lactogen I, rat
• Prolactin
• Placental Lactogen

Topics

• Animals
• Animals, Suckling
• Body Weight
• Choriocarcinoma (chemistry)
• Feedback
• Female
• Hypothalamus
• Lactation (physiology)
• Neoplasm Transplantation
• Placental Lactogen (genetics, pharmacology)
• Pregnancy
• Prolactin (blood, pharmacology)
• RNA, Messenger (analysis)
• RNA, Neoplasm (analysis)
• Rats
• Rats, Sprague-Dawley
• Sheep
• Uterine Neoplasms (chemistry)