Administration of progesterone causes a significant increase in body weight in adult female rats (Hervey, 1964; Hervey & Hervey, 1964) and mice (Dewar, 1964). Chlormadinone acetate (17α-acetoxy-6-chloropregna-4,6-diene-3,20-dione = CAP) seems to have a similar effect in cattle (Takeuchi, Shimizu, Toyoda, Kawai & Adachi, 1966) and rats (Shimizu & Ishibashi, 1965, unpublished results). The weight gains of adult female rats treated with CAP was therefore compared with that of controls and progesterone-treated rats.
Nulliparous adult rats of the Wistar strain, aged about 3 months, were used. They had free access to a pelleted diet containing 20% crude protein; green vegetables were given once a week. Vaginal smears were examined daily between 9.00 and 10.00 hr. Four groups of 13 rats were set up: untreated controls, controls injected with the vehicle only, CAP-treated rats and progesterone-treated rats. Both steroids were given in doses of 5 mg., s.c. once daily, as a 10 mg./ml.