Development of Female Characteristics in Adult Male Rabbits Following Prolonged Administration of Estrogenic Substance

Estrogenic substance was prepared by extracting acidulated human pregnancy urine with butyl alcohol in a continuous extractor as described by Veler, Thayer, and Doisy. 1 The alcohol was removed by distillation, using a vacuum pump, and the residue dissolved in ethyl ether. The ether extract was added to olive oil, and the ether evaporated. The resulting olive oil solution was then assayed for its estrogenic content by the technique of Coward and Burn. 2 The quantity required to produce estrus in 50% of 20 ovariectomized, sexually mature, albino rats constituted the rat unit used in the following experiment.

Twenty-four male albino rabbits of known parentage, 16–17 months of age, were employed. Eight of these were injected subcutaneously once a day, 6 days a week, with from 20–60 rat units of estrogenic substance in olive oil. Injections were continued in 6 animals for 250 days or more. Eight rabbits were injected in like manner with plain olive oil, and 8 were left untreated. All animals had a syphilitic infection given in connection with another experiment in which they were being used. Only those rabbits receiving injections of estrogenic substance showed the variations from the normal described below.

Mammary glands. Hypertrophy of nipples to the size of those of the lactating female rabbit developed after 80 days of treatment. Milk could be expressed from the nipples. In 6 animals, the secretion increased in amount and became thick and white, in 2 animals it remained thin and watery. After continuing for at least 90 days in all animals, lactation decreased, and the nipples became smaller. Subsequently, milk could be expressed only from a few nipples in most of the animals, and in one case it disappeared entirely after being present for 120 days.