Oestradiol-decanoate, dissolved in arachis oil and orally administered to rodents, produces oestrogenic effects. Compared on a molecular basis the ester has 0.1-1.0 times the activity of ethinyl oestradiol, dependent on the species and the parameter studied. The effects of oestradiol-decanoate are less or absent when the oil is omitted. It is likely that absorption of the steroid ester takes place via the intestinal lymphatics in conjunction with the oil.
PIP: The estrogenic activity of a microcrystal suspension of ethinyl estradiol was compared with estradiol-17beta-decanoate dissolved in arachis oil and orally administered. Rats, mice, hamsters, and guinea pigs were studied in regard to: 1) vaginal cornification, 2) weight and intraluminal uterine fluid of the uterus, 3) vaginal opening, 4) ovulation, and 5) pituitary gonadotropin secretion. In ovariectomized rats, estradiol-decanoate in oil had approximately .75 times the activity of ethinyl estradiol in effects on vaginal cornification; for mice it was .125 and for hamsters, .25. Based on uterine weight and uterine fluid in immature rats, estradiol-decanoate was .08-.09 times as active as ethinyl estradiol. with respect to inhibition of ovulation in ovariectomized guinea pigs, estradiol-decanoate displayed about .25-.50 times the activity of ethinyl estradiol. Estradiol-deca was capable of suppressing the increased secretion of gonadotropins by the pituitary of the ovariectomized partner in parabiotic rats, resulting in a decreased ovarian weight in the intact partner. It is likely that the absorptono of the steroid ester takes place via the intestinal lymphatics in conjucntion with the oil.