Abstract
The authors previously reported1, 2) that the post-partum ovulation in the rats occurred from 12 hrs to 30 hrs after delivery, and then, in the rats delivered from 10:00 to 20:00 that ovulation was blocked with Nembutal administration (subcutaneously) between delivery time and 2 hrs after delivery.
This experiment was carried out to determine the follicular development and oocyte maturation with special reference to the time of the release of ovulating hormone (OH) in normal cyclic, HCG treated and post-partum rats. Adult virgin female rats of the Wistar strain were kept under 12 hrs light and 12 hrs darkness (light on 6:00, light off 18:00) and 25°C room. Vaginal smears were taken daily and only animals which had shown more than 3 times consecutive 4-days estrous cycle were used.
OH potency of the anterior pituitary was expressed as number of rats ovulating per the animals injected with test sample on the 2nd day of diestrus (D2).
In proestrous rats, OH potency of the anterior pituitary at 11:00, 13:00 and 14:00 was 6/6, 4/5 and 4/5, respectively, but the potency began to decrease from 15:00 (2/5), and then it disappeared at 19:00 (4/5).The changes of the nucleus of the oocyte began from 2 hrs after the time expected for the release of OH, and the ovulation points were observed at 12 hrs after OH release (correspond to 2:00 on the day of estrus). The intraperitoneal administration of Nembutal at 13:30 on proestrus did not decrease in OH potency and it also prevented the maturation division in the change of oocyte maturation.
In the rats delivered between 10:00 and 20:00, OH potency at 0, 1, 2, 4 and 6 hrs after delivery was 10/10, 3/3, 4/7, 3/5 and 0/5, respectively.
The breakdown of germinal vesicle was first observed 4 hrs after delivery.
It is suggested that only brief exposure of the follicles to OH is essential for the initiation of maturation division of the oocyte.
In estrous cycle, the follicles over 550 μin diameter had suddenly developed during the time between D2 and proestrus. Also, larger follicles than 550 p in pre-or post-partum rats grew rapidly from the 22nd day of pregnancy to delivery time.
It was found that the follicular development and the oocyte maturation in post-partum pro-ceeded quite similar to that in estrous cycle.
Further, process of the oocyte maturation in the rat treated with HCG on D2 was similar to that in proestrus of the normal cyclic rat.
The time of OH release could be estimated from the number of normal follicles (over 550 μ) showing normal maturation changes.
It is suggested that OH may be released 2 to 4 hrs after delivery which has occurred between 10:00 and 20:00 in the rats.
