Vaginal Stimulation and Progesterone: Relation to Corpora Lutea Maintenance, Pregnancy and Parturition in the Hamster

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Abstract
In unmated hamsters made pregnant, assisted by a single injection of progesterone at the time of artificial insemination, corpora lutea regressed and ovarian weight was adversely affected. Despite this early regression of corpora lutea and ovarian insult, these females remained pregnant until term when an inhibition of parturition was noted. In contrast, among normally mated females or those whose vaginae were stimulated artificially the corpora lutea did not regress nor were the ovaries affected. In these females, parturition proceeded normally. We interpret our findings to indicate that progesterone inhibits gonadotropin release which is necessary for the functional maintenance of the ovary and corpora lutea during pregnancy. This progesterone, however, persists sufficiently to maintain the pregnancy. This dual action of progesterone; detrimental for the corpora lutea, ovary and hypothalamic-pituitary complex while supportive to pregnancy per se, also inhibits some factors necessary for parturition. Adequate stimulation of the vagina, however has the effect of mitigating against the adverse effects.