Effect of Ovariectomy on Egg Transport in the Rabbit

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Abstract
The importance of pre- and postovulatory ovarian steroid secretion on egg transport through the entire oviduct was studied in the rabbit. Estrous New Zealand rabbits were induced to ovulate with human chorionic gonadotropin (hCG), had eggs transferred to the oviducts, were bilaterally ovariectomized and had eggs transferred to the oviducts, or were induced to ovulate with hCG and were bilaterally ovariectomized shortly after ovulation. Groups of animals so treated were sacrificed at either 48 h or 72 h after ovulation or egg transfer. The oviductal recovery of eggs and the distance traveled by the eggs was determined. Eggs transferred to the oviducts of estrous rabbits were transported rapidly; only 15.9 ± 9.7 percent of the eggs could be recovered from the oviducts of estrous rabbits 48 h after transfer. In contrast, between 72 percent and 86 percent of the eggs were still located in the oviducts in the other groups sacrificed at a similar time. By 72 h after egg transfer or ovulation no eggs could be found in the oviducts of estrous rabbits, and only 8.6 ± 4.8 percent of the eggs were located in the oviducts of rabbits induced to ovulate with hCG. However, if estrous rabbits were bilaterally ovariectomized immediately before egg transfer or were ovariectomized shortly after hCG-induced ovulation approximately 40 percent of the eggs were still located in the oviducts at 72 h. The results demonstrate that egg transport through the entire oviduct is fastest in estrous rabbits, and that acute steroid withdrawal (ovariectomy) and normal preovulatory steroid changes act to impede egg transport rates. However, steroid withdrawal by itself is not sufficient to cause normal egg transport. It appears that preovulatory steroid surges are important for subsequent normal egg transport. When rabbits were ovariectomized shortly after ovulation egg transport was delayed. The data suggest that preovulatory steroid surges and/or steroid withdrawal induce an impeding effect on egg transport, and that postovulatory steroid secretion changes are essential to overcome this impeding effect and facilitate normal egg transport through the entire oviduct.