Studies of the components of an oral contraceptive agent in albino rats. II. Progestogenic component and comparison of effects of the components and the combined agent

In a study conducted on albino rats over 2 years, norethindrone acetate, a progestogenic component of oral contraceptives, was administered at doses 10 to 100 times higher than the human equivalent. The study found dose-related effects such as growth retardation, alopecia, and enhanced survival rates. Male rats experienced testicular and gonadal atrophy, while females showed uterine changes, increased adrenal gland weights, decreased ovarian weights, and ovarian atrophy. High doses led to liver enlargement and cystic mastopathy in both sexes, with females developing more uterine polyps and both sexes showing increased liver neoplastic nodules. Despite these changes, there were no significant differences in tumor incidence or development compared to untreated rats, and females exhibited a delayed onset of tumor formation.