Estrous cycle-dependent changes in the expression of aromatic hydrocarbon receptor (AHR) and AHR-nuclear translocator (ARNT) mRNAs in the rat ovary and liver

The aromatic hydrocarbon receptor (AHR) and AHR nuclear translocator protein (ARNT) mediate the toxic effects of a wide variety of halogenated and polycyclic aromatic hydrocarbons. While it can be assumed that AHR has an endogenous function, its role in reproduction is currently undefined. The present study seeks to examine the regulation of AHR and ARNT mRNAs in liver and ovarian tissues across the rat estrous cycle. Message for hepatic AHR was increased significantly on the morning of proestrus, and decreased dramatically by the evening of proestrus; while hepatic ARNT mRNA was significantly decreased between diestrus and the morning of proestrus, and between the evening of proestrus and the morning of estrus. Ovarian AHR mRNA was unchanged from diestrus to proestrus, and was decreased on the evening of proestrus. Changes in the expression of ARNT mRNA mirrored changes in the liver. To assess interaction between the AHR- and estrogen-receptor (ER)-signaling pathways and to test the hypothesis that estrogen regulates AHR mRNA, 25-day-old female rats were injected with either 17 beta-estradiol, the ER antagonist ICI 182 780, or with vehicle, and hepatic AHR mRNA was measured. Treatment with estrogen or the estrogen antagonist did not alter the abundance of AHR mRNA in the liver. These data suggest that while estrogen may not be the key regulator of AHR mRNA expression, a factor associated with the rat reproductive cycle may be important in regulating the expression of both the AHR and ARNT genes in the ovary and liver. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.