Localization and activity of adrenal carbonyl reductase during the estrous cycle

Changes in carbonyl reductase (CR) activity towards seven substrates in adrenal glands of female rats were investigated during estrous cycle and the circadian patterns of adrenal CR activity towards seven substrates in male rats were examined. The localization of the enzyme protein in the adrenal gland was carried out by immunohistochemistry. In female rats, adrenal CR activity was lowest between 1200 and 2000 h on the day of proestrus, the phase in which a large, significant increase in ovarian steroids, gonadotropins and prolactin is observed. Immunoreactivity in the zona reticularis of the adrenal cortex to anti-adrenal CR, CR-K2, antibody on the day of proestrus was faint or negative compared with that on other days of the estrous cycle. In male rats, no major changes in adrenal CR activity were observed compared with females, although these were slight changes in all the enzyme activities. These results suggest that adrenal CR may be negatively regulated by the pituitary-adrenal axis in female rats and, in particular, on the day of proestrus.