Inhibition of the preovulatory LH surge after a catecholestrogen (2-hydroxyestrone) antiserum injection in the third ventricle of cycling female rats

Sex differences in cytochrome P450 1B1, an estrogen-metabolizing enzyme, in the rhesus monkey telencephalon

The metabolic enzyme CYP1B1 is a recently cloned member of the cytochrome P450 superfamily, expressed widely throughout primate tissue, including the CNS. Although CYP1B1 protein is known to metabolize estradiol to catecholestrogens in the uterus, its localization and function in brain have not yet been described. To better understand CYP1B1 distribution, we have combined in situ hybridization (ISH) for its mRNA with immunohistochemistry (IHC) for the CYP1B1 protein in selected brain regions of male and female adult rhesus monkeys (Macaca mulatta). Blocks of formalin-fixed tissue obtained from the frontal cortex, hippocampus, thalamus, and amygdala were processed and embedded in paraffin. They were then sectioned and stained as described for human tissue [Muskhelishvili, L., Thompson, P.A., Kusewitt, D.F., Wang, C., Kadlubar, F.F., 2001. In situ hybridization and immunohistochemical analysis of cytochrome P450 1B1 expression in human normal tissues. J. Histochem. Cytochem. 49, 229-236]. Results indicated widespread distribution of CYP1B1 mRNA in both male and female monkey frontal cortex, hippocampus, thalamus, and amygdala. In contrast, although CYP1B1 protein was co-localized with its mRNA in the female brains, it was primarily restricted to hippocampal pyramidal neurons in the male brains. These results suggest that CYP1B1 may subserve widespread metabolic functions in the female primate brain but have more restricted actions within the hippocampal pyramidal neurons of the male.

Inhibition of catechol estrogen formation in rat liver microsomes by hormonal steroids and related compounds

The inhibitory action of a number of different hormonal steroids and related compounds on the 2-hydroxylation of estradiol by male rat liver microsomes was examined by a radiometric assay. Progesterone, Diethylstilbestrol, testosterone and 4-androstenedione were found to be the most potent of the compounds tested but inhibition was also observed with other steroids and a group of androgen analogs which are aromatization inhibitors. The kinetic constant Ki for those steroids which gave linear double reciprocal plots when added to [2-3H]estradiol was determined and the products from [14C]estradiol in the presence of the inhibitors were examined by TLC and autoradiography. The addition of steroids with a 17-hydroxyl group such as testosterone or dihydroequilin resulted in the formation of mainly 2-hydroxyestradiol with smaller amounts of other metabolites while those with a reducible ketonic group such as progesterone, 4-androstenedione, equilin or equilenin gave rise to considerable amounts of estrone in addition to the catechol estrogens. Further purification of the liver microsomes did not alter this effect. The possible role of progesterone and the catechol estrogens in the control of estrogen hydroxylation in liver as well as other aspects of steroid interaction are discussed.