Abstract
The levels of pituitary gonadotrophins (follicle stimulating hormone and luteinizing hormone) activities, the ovarian weight and the ovarian ascorbic acid level were estimated in pregnant and lactating rats. The level of pituitary follicle stimulating hormone activity rose sharply in the second half of gestation, and reached the peak on day 19 of pregnancy, and then dropped abruptly prior to the day of labor. The ovarian weight fluctuated almost coincidentally with the pituitary follicle stimulating hormone activity. The level of pituitary luteinizing hormone activity fluctuated with two peak values. It reached the first peak on day 14 and the second peak on day 19, and dropped abruptly prior to the day of labor. The ovarian ascorbic acid content fluctuated reversely with the fluctuation of pituitary luteinizing hormone activity until day 18. The content continued to decrease until the day of labor. These results suggested that a) the anterior pitutiary maintained its activity during pregnancy; b) three days before the onset of labor, it started to release luteinizing hormone and two days before that, it started to decrease in release of follicle stimulating hormone; and c) pregnancy terminated following decrease of circulating follicle stimulating hormone activity and sharp increase of circulating luteinizing hormone activity.
