Vaginal stimulation and progesterone: relation to corpora lutea maintenance, pregnancy and parturition in the hamster.

Abstract

Hamster ovaries were examined under various natural and experimental conditions involving progesterone administration and its possible influence on parturition was oncsidered. Pregnancy was artificially induced in some without vaginal stimulation and 5 or 10 mg of progesterone were given. In others vaginal stimulation was done and the same doses of progesterone given at the time of artificially induced pregnancy. OVaries were removed on Day 5 9 or 13 and following parturition on Day 16. If parturition did not occur on Day 16 ovaries were removed on Day 17. Oxytocin given on Day 17 to females overdue in delivery had no effect. In females made pregnant without vaginal stimulation but with progesterone given all corpora lutea had regressed by Day 9 and ovarian weight had diminished. Those having received 10 mg of progesterone showed earlier changes in ovaries and corpora lutea. All these females remained pregnant until term but then an inhibition of parturition was noted. Mature Graafian follicles were present in all ovaries. In those whose vaginae had been stimulated artificially and progesterone given at the time of induced pregnancy the corpora lutea did not regress nor were the ovaries affected. In these females parturition proceeded normally. It is thought that progesterone inhibits gonadotropin release necessary for the functional maintenance of the ovary and corpora lutea. Some of the progesterone however persists to adequately maintain pregnancy. A factor necessary for parturition is also inhibited by progesterone. Adequate stimulation of the vagina prevents these adverse effects. Vaginal stimulation is thought to activate the luteotropic complex. In the hamster normal gestation and parturition seem to require a continued supply of luteotropic hormones and possibly ovarian factors for parturition.