Studies on shortening of estrous cycle in 4-day cyclic mice

III. Effect of male proximity on in-duction of ovulation by the progesterone treatment

Abstract

The effect of male proximity on induced ovulation by progesterone in the 4-day cyclic female mice was studied.
The animals were housed in artificially illuminated animal rooms (light: 5 a.m. to 7 p.m.).
In this experiment, the 4-day cyclic mice which has not been exchanged at a 3-day oestrous cycle by pre-test of male proximity were used.
The female mice were divided into 2 groups. One of them were placed adjacent to male mice with partition of the wire net in a cage. The others were served as a control and male mice were not employed for this group.
Progesterone was once injected subcuteneously into the female mice of the both groups at 4 p.m. or 7 p.m. on the day of diestrous stage and induced ovulation was examined in the following day (the day of expected proestrous stage). The doses of progesterone were 0.130.25 mg or 0.5 mg per mouse at 4 p.m. or 7 p.m., respectively.
Induction of ovulation due to progesterone was more pronounced in the mice approached by the male mice as compared with the control mice (Fig. 1).
The results obtained were comparable to those of the preceding experiment in which ovulation was enhanced by pretreatment with estradiol prior to progesterone administration.
Thus, it is suggested the male proximity might induced the secretion of estrogen in the female mice.