This Article Full Text Full Text (PDF) All Versions of this Article: 147/5/2575    most recent Author Manuscript (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bridges, R. S. Articles by Byrnes, E. M. Search for Related Content PubMed PubMed Citation Articles by Bridges, R. S. Articles by Byrnes, E. M.

Reproductive Experience Reduces Circulating 17ß-Estradiol and Prolactin Levels during Proestrus and Alters Estrogen Sensitivity in Female Rats

Department of Biomedical Sciences, Tufts University, Cummings School of Veterinary Medicine, North Grafton, Massachusetts 01536

Address all correspondence and requests for reprints to: Dr. Robert S. Bridges, Department of Biomedical Sciences, Tufts University School of Veterinary Medicine, 200 Westboro Road, North Grafton, Massachusetts 01536. E-mail: robert.bridges{at}tufts.edu.

The reproductive experiences of pregnancy, parturition, and lactation affect a range of neural and endocrine processes after the end of lactation. In women, previous parity results in reduced circulating prolactin (PRL) and androgen levels years after giving birth. Reductions in PRL secretion also occur in reproductively experienced, female rats. In the present study we examined the status and regulation of estradiol (E₂) and PRL during the reproductive cycle after reproductive experience. These hormones regulate one another and have been implicated in a number of disease and aging processes. Using a rat model, the patterns of E₂ and PRL secretion, pituitary PRL content, and estrogen receptor expression were characterized from 1200–1800 h on proestrus in age-matched, primiparous and nulliparous animals. The possible effect of parity on estrogen sensitivity was then examined by challenging nonlactating, ovariectomized, age-matched, multiparous and nulliparous rats with estradiol benzoate (EB; 0, 1, 5, 25, and 125 µg/kg) and measuring PRL responses 24 and 48 h later. Previous parity resulted in modest, yet significant, reductions in E₂ and PRL levels on proestrus, a limited increase in pituitary estrogen receptor expression, and a significant shift in estrogen sensitivity, as measured by EB-induced PRL secretion. Nulliparous animals were more sensitive than multiparous rats to the two lower doses of EB, whereas multiparous animals were more responsive to the highest EB dose. These unique parity-induced alterations in the female’s endocrine state that persist beyond lactation may impact a multitude of estrogen-mediated processes over the female’s adult life span.

This article has been cited by other articles:

				B. R. Andrade, A. A. K. Salama, G. Caja, V. Castillo, E. Albanell, and X. Such Response to Lactation Induction Differs by Season of Year and Breed of Dairy Ewes J Dairy Sci, June 1, 2008; 91(6): 2299 - 2306. [Abstract] [Full Text] [PDF]

				K. Britt, A. Ashworth, and M. Smalley Pregnancy and the risk of breast cancer Endocr. Relat. Cancer, December 1, 2007; 14(4): 907 - 933. [Abstract] [Full Text] [PDF]

				G. M. Anderson, D. R. Grattan, W. van den Ancker, and R. S. Bridges Reproductive Experience Increases Prolactin Responsiveness in the Medial Preoptic Area and Arcuate Nucleus of Female Rats Endocrinology, October 1, 2006; 147(10): 4688 - 4694. [Abstract] [Full Text] [PDF]