Enhancement of aromatase gene expression in the mediobasal hypothalamus during anestrus in the beagle bitch

The relationships among expression of cytochrome P450 aromatase (P450arom) mRNA in the mediobasal hypothalamus (MBH), ovarian aromatase activity, and estrogen secretion were examined throughout the estrous cycle in beagle bitches. Using polymerase chain reaction (PCR) analysis we were able to detect P450arom gene transcripts in the canine MBH. The level of hypothalamic P450arom mRNA increased during the progression of anestrus and declined thereafter. Ovarian P450arom activity, as measured by a (H2O)-H-3 assay, were low in anestrus, increased in proestrus, and declined thereafter. Ovarian P450arom activity and plasma estradiol-17beta levels were positively correlated (r = 0.77, P < 0.05). These results suggest that enhancement of hypothalamic P450arom gene expression is associated with termination of anestrus. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.