Initiation and control of ovulation in the mouse luteal phases. Effects of oestrogen, progesterone and prolactin.

The aim of the present study was to examine the effect of exogenous oestrogen and progesterone on ovulation in early pregnant mice and at the end of pseudopregnancy. The results demonstrate that there are mature follicles during early pregnancy which were induced to ovulate by administration of large doses of oestrogen (greater than or equal to 10 micrograms) on day 4 of pregnancy. Ovulation was also induced by inhibition of progesterone secretion with bromocriptine. If progesterone or prolactin was given in conjunction with bromocriptine, the ovulation effect was abolished. At the end of pseudopregnancy, the spontaneous ovulation was inhibited by injections of progesterone (1.0 mg). Oestrogen given by itself at the end of pseudopregnancy caused the animals to mate earlier than the control animals. This confirms the presence of mature follicles in mice during pregnancy and suggests that the LH peak needed for ovulation can either be provoked by administration of oestrogen or by blocking of progesterone.