Effects of Progesterone and Related Compounds on Fertilization, Transportation and Development of Rabbit Eggs

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Abstract
Isolated mature rabbits were treated with progesterone or other related compounds for 3 days before insemination and an ovulating injection of HCG [human chorionic gonadotropin]. They were examined on various days later to ascertain the fertilization, transportation and development of eggs. Subcutaneous injection of 1-4 mg progesterone/rabbit reduced the fertilization rate from 66 to 22%; feeding with 1-4 mg medroxyproges-terone acetate from 88 to 51%; with 0.2 to 20 mg chlormadinone from 66 to 2%, while feeding with 2-4 mg norethynodrel, norethindrone acetate, or methyltestosterone had no effect. The rate of egg recovery in terms of C.L. [corpora lutea] was low (51-82%) and the presence of eggs in the uterus on day 2 was high (27-82%) in the animals treated with progesterone and its derivatives. The disturbance of fertilization appears closely related to the rapid egg transport. Many fertilized or unfertilized eggs recovered from the uterus were degenerating and a few eggs were recovered from the vagina. Uterine or tubal insemination increased the fertilization rate (38-55%) compared with vaginal insemination (23%) in treated animals but was still far below that of untreated animals (78-91%). Thus, sperm transport appears to be disturbed to a certain extent. When sperm were incubated in the uterus or tube of the treated animals for 12 hr, recovered and deposited into the tube of newly ovulated rabbits, capa-citation of sperm was probably inhibited to some degree but fertilization of eggs was still possible. Although the fertilization rate was quite high following administration of 1 mg progesterone or 0.2 mg chlormadinone (66%), practically all the eggs had degenerated by day 6. Similarly, treatment with 4 mg norethynodrel also induced degeneration of eggs by day 6. It is concluded that treatment of rabbits with progestational compounds has the effect of disturbing sperm transport and sperm capacitation, thus inhibiting fertilization to a certain degree; but their major effect is on the transportation of eggs, causing some disturbance of fertilization, but mainly causing the degeneration of eggs in the uterus and their expulsion from the uterus.