Abstract
The present article deals with some observations on hormone-induced polyovulation and pregnancy in mature and immature rats, with special reference to the number of ovulated eggs and pregnancy.
The rats used are of Wistar/Mk strain; they are 35 and 60 days in age, and females were all virgin. The average number of ovulated eggs from 10 females of this strain was found to be 8.4, and that of litter-size was 6.5 in the natural oestrus cycle.
The female rats in various stages of the oestrus cycle received an intramuscular injection of pregnant mare's serum (PMS) and 44hr. later an injection of human chorionic gonadotrophin (HCG).
1) Mature females: The following four doses, 20 i.u., 40 i.u., 80 i.u. and 100 i.u., of PMS and HCG, were applied. After treatment, they were mated by being placed with males at a rate of 1_??_: 2_??_. In the following morning, the females were inspected for presence of the copulatory plug in their vaginas, and some of them were sacrificed for examining induced ovulation.
The number of mated females showed no significant difference by doses here applied (Table 1). The number of eggs was significantly larger after injection with 40 i.u. PMS and HCG than after injection with other doses. The number of eggs extruded in the oviduct was 268 in total, being variable from 14 to 48 by individual and 20.6 on an average (Figs. 1, 2). The results are striking in showing a remarkable polyovulation, since the number of eggs extruded in natural ovulation was 8.4 on an average (Table 1).
Microscopical examinations revealed that fertilized eggs in induced ovulation were normal in process of development (Figs. 3_??_5).
Approximately fifteen out of ninety-seven females which mated in response to the injected gonadotrophins became pregnant. This number was less than that of pregnant females after the natural oestrus (Table 2). Most females failed to produce live young, but six females gave litters with a 7.3 averaged litter-size close to the control value.
2) Immature females: Injection of 20 i.u. PMS and HCG was made in immature females. Eight out of thirty-five females received injection showed vaginal opening 40 to 60 hours after the injection of PMS. But, there occurred no mating and no eggs were obtained from all treated immature females. Further investigations are needed to learn the optimum dosage of PMS in order to induce the ovulation and to produce live young, with special regard to the time-relation of the combined injection of two hormones in relation to the oestrous cycles of animals.
