Effect of norethisterone oxime on ovum transport and development, and on morphology of oviduct in rabbits.

The effects of norethisterone oxime (NETO) on ovum transport and development, and on morphological changes of oviducts in rabbits were studied to evaluate the mechanism of its anti-implantation action. NETO 2 mg/kg/day was given to mature rabbits from day 1 through day 3 or from day 2 through day 4 of pregnancy by gavage. The animals were anesthesized after various hours of administration, the oviducts were dissected out and divided into 6 equal segments. Ova in each segment and sometimes those in the uterus were collected by flushing the tube with saline. The ova were then observed microscopically for normality. Histological sections were made from different portions of the oviducts, stained with HE and PAS and examined microscopically. Recovery rate of ova was generally lower than that in control animals. Ovum transport was first accelerated and then retarded or even blocked. Ova which eventually entered the uterus might develop into blastocysts, but they were smaller in size. Mucin coat of ova markedly reduced in thickness. Mucin secretion from epithelial cells was less. Some degenerated ova appeared in the oviducts. The oviducts were tortuous, hyperplasia existed in the epithelial cells. The mucosa exhibited edema, and the circular muscle layer thickened without increase in the number of muscle cells. This indicated a status of muscular contraction. Dilatation and congestion of capillaries appeared in the muscular layers and serosa. All these manifestations were so prominent that the lumen of ampullary isthmic junction and isthmus portion was significantly narrowed and the transportation of ova thus blocked. The changes caused by NETO were very similar to those caused by exogenic estrogen. It is suggested that anti-implantation action of NETO in rabbit experiment is mainly related to its estrogenic activity.