The ovulation time of rats was estimated by successive laparotomies at intervals of 6 hr starting from 6 AM on the day of estrus. A dose of pentobarbital sodium, 30 mg/kg body weight, given at 1:30 PM caused a delay of ovulation for approximately 24 hr in 11 of 12 females, while 2 out of 8 females receiving a dose of 20 mg/kg ovulated between 6 AM and noon on the day of estrus. After initial treatment during proestrus with a dose of 30 mg/kg of pentobarbital sodium, additional amounts administered on succeeding days of estrus also delayed ovulation, depending upon dose. Females with ovulation delayed for 1 or 2 days were mated; the proportion of fertilized eggs and the morphology of fertilized eggs were not affected, except that a high incidence of supplementary sperm was observed. The rats with ovulation delayed for 1 day showed normal fertility; ovulation delayed for 2 days was followed by a slight reduction in the number of implantation sites and viable fetuses. (Endocrinology84: 1456, 1969)
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Toyoda et al. (1969) studied this question.