No abstract

Bilateral ovariectomy (Ovx) was carried out on day 20 of pregnancy in Mongolian gerbils (Meriones unguiculatus). The body weights of all groups tended to decrease on the day after the operation, and the decrease was significant in the group that was ovariectomized and given vehicle (Ovx + vehicle group). The body weight in this group never recovered until autopsy on day 24, which is normally 1 day before parturition. No fetuses survived to the time of autopsy in any of the animals of the Ovx + vehicle group. Daily administration of 4 mg of progesterone (P 4 ) prevented the termination of pregnancy in Ovx animals, but 1 mg did not. Treatment with estradiol 17b (E 2 ) in addition to 4 mg of P 4 tended to result in a lower rate of fetal survival than that of the Ovx group treated with 4 mg of P 4 alone. With regard to fetal weight, treatment with 4 mg of P 4 resulted in the same weight as in the sham-operated controls, but the addition of 0.2 or 1 mg of E 2 to the 4 mg of P 4 resulted in a significantly lower weight than that of fetuses in the 4 mg of P 4 group. The present study suggests that adequate maintenance of pregnancy in ovariectomized gerbils can be achieved by daily treatment with 4 mg of P 4 alone. Moreover, treatment with 0.2 or 1 mg of E 2 in addition to 4 mg of P 4 caused a deterioration in the maintenance of gestation, in contrast to the effects in rats, mice and hamsters.