Effect of long-term administration of norethisterone (a progestogen-only contraceptive) on the female genital tract of the albino rat.

Effect of norethisterone (a progestogen-only contraceptive) treatment (0.5 mg/rat daily for 75 days) on the genital tract (viz., ampulla, uterus, cervix and vagina) of cycling female rat was evaluated from histometric and karyokinetic investigations. Long-term administration of this synthetic progestin resulted in decrease of epithelial height in the ampulla and increase of epithelial height and/or epithelial per cent in the uterus (endometrium and uterine gland) and vagina. It also increased the uterine myometrical per cent with decrease in stromal per cent. Persistence of mucous layer in the cervix and vagina was markedly evident after norethisterone treatment. Norethisterone inhibited the mitotic rate in all the regions of the genital tract except in the uterine gland where it was increased. The findings suggest that norethisterone disturbs the normal physiology of the genital tract, thereby preventing conception in the albino rat.