Expression of estrogen receptor α and β genes in the mediobasal hypothalamus, pituitary and ovary during the canine estrous cycle

Estrogen receptor alpha (ERalpha) and ERP mRNA levels were measured in the mediobasal hypothalamus, the anterior pituitary and the ovary of beagle bitches at various stages of the estrous cycle. With polymerase chain reaction analysis we detected ERP gene transcripts in all tissue samples. The levels of hypothalamic and pituitary ERalpha and beta mRNAs increased from mid anestrus to proestrus and declined thereafter. In the ovary, ERa mRNA levels increased from proestrus to diestrus and were positively correlated with plasma progesterone levels (r = 0.62, P < 0.01), whereas ERP mRNA levels increased from mid anestrus to proestrus and were positively correlated with plasma estradiol-17beta levels (r = 0.73, P < 0.001). These results suggest that the rise in hypothalamic and pituitary ERalpha and P mRNAs is associated with termination of anestrus, and that increases in ovarian ERalpha and beta mRNAs may be involved in initiating development of the follicle or corpora lutea. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.