Inhibition of Ovulation by Systematically Administered Actinomycin D in the Hamster

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Abstract
Actinomycin D (AMD) (60 [mu]g/100 g body wt) was administered by intraperitoneal injection into both adult and immature female hamsters. In adult animals in which human chorionic gonadotropin (HCG) was given to promote the occurrence of ovulation, AMD had a strong inhibitory effect when injected up to 5 1/2 hr. later, but none at 7 1/2 or 9 1/2 hr. Similarly, in immature hamsters induced to ovulate with pregnant mares'' serum gonadotropin (PMS and HCG, inhibition was effected by AMD given within 6 hr. of the HCG treatment, but not at 8 hr. or later. The findings are consistent with the view that systematically administered AMD inhibits ovulation by acting peripherally, possibly by the same mechanism as that previously proposed for AMD introduced into ovarian follicles, namely, by suppressing the formation of mRNA involved in the induction of ovulation. If this is true, it can be surmised that production of mRNA in the hamster is complete by about 6 hr. after HCG injection.