Increased activity of ovarian thecal cytochrome P45017α in the hamster induced by endogenous LH

Abstract

The in vivo regulatory action of LH on the ovarian androgen synthesizing enzyme cytochrome P450(17 alpha) (17 alpha-hydroxylase/C17,20-lyase) was studied in cyclic golden hamsters. Immunohistochemical studies using anti-porcine testicular cytochrome P450(17 alpha) antibody indicated that the enzyme was limited to thecal cells. Transient removal of the negative feedback action of endogenous steroids by use of aminoglutethimide phosphate produced an increase in endogenous gonadotropins. A single dose (30 mg) of aminoglutethimide on days 1, 2 or 3 of the estrous cycle (day 1 = estrus), increased serum levels of LH, but only for about 12 h. Increases in enzyme activities, which persisted for at least 24 h, followed. Two doses of aminoglutethimide, 12 h-apart, maintained elevated levels of serum LH for about 36 h, and enzyme activities for at least 48 h. However, when the drug was given after the pre-ovulatory surge of LH on proestrus, and again on the morning of estrus, neither serum LH nor enzyme activity levels increased within 24 h. Induced increases in enzyme activity had no effect upon ovulation rate, as determined by the number of oviductal eggs present on the morning of estrus. The results demonstrate clearly a close correlation between serum concentrations of LH and ovarian androgen synthesizing enzyme activity.