Temporal Changes in Ovarian Steroid-17 -hydroxylase in Immature Rats Treated with Pregnant Mare's Serum Gonadotropin

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Abstract
Steroid 17α-hydroxylase was measured, using a tritium exchange assay, in the microsomal fraction of ovaries from immature intact or hypophysectomized rats exposed to 20IU pregnant mare's serum gonadotropin. The hypophysectomized animals were pretreated with diethylstilbestrol (DES) to increase the ratio of granulosa:theca + interstitium in the ovary; controls received oil vehicle. In intact animals hydroxylase levels decreased within 8 hr after injecting PMS but by 48 hr the concentration was more than 3 times that found in starting controls; after 48 hr the enzyme level decreased drastically and remained low through 120 hr. In oil-treated hypophysectomized rats hydroxylase activity decreased within 12 hr after PMS but in DES-treated animals the enzyme was already extremely low. In both, the enzyme level reached much higher levels than in intact animals and it did not decrease significantly through 72 hr after PMS. The results indicate that 17-hydroxylase activity is induced by PMS treatment but that the enzyme is actively destroyed beginning at 48 hr in intact animals; this could account for the decrease in estrogen and androgen production associated with the ovulatory surge in gonadotropins which occurs on the second day after PMS injection.