The Action of Clomiphene in the Ewe

Abstract

Three tests are described, two each with thirty-six entire and one with fifty-six spayed ewes, in which the action of clomiphene citrate was characterized in the sheep. It was found to suppress pituitary activity, to induce behavioural oestrus and to have a grossly stimulatory action on the uterus in that it induced a high incidence of hydrops uteri. It is concluded that clomiphene acts in the ewe as a weak oestrogen but differs qualitatively from true oestrogen in its effect on the uterus.

Effect of Clomiphene Citrate on Follicular Recruitment, Development, and Superovulation During the First Follicular Wave in Rahmani Ewes

“…Further, to support this concept, clomiphene and its isomers are estrogenic in some species and antiestrogenic in others; these varying properties have been observed in different organs, tissues, and cell types (9). In intact ewes, clomiphene inhibited ovulation but induced estrous (7), which suggested that different regions of the brain respond differently to clomiphene or its isomers (10). Similar findings were observed in rabbits; CC maintained normal follicular growth and development, but inhibited ovulation in rabbits (6).…”

“…This effect induces a significant increase in the secretion of GnRH and subsequent secretions of FSH and LH (11). Contrary to this, ovarian activities were inhibited in the ewes, i.e., the follicles failed to develop, ovulations did not occur, and the corpora lutea were not formed (7). No pituitary-stimulatory or gonadotropin-like activity was observed in sheep and rats treated with CC (5,9).…”

“…Unlike in rodents, in rabbits, ovulation can be triggered by injection of human chorionic gonadotropin (hCG) after CC treatment (6). In ewes, CC acts as a weak ERM, which inhibits ovulation and induces estrous without ovulation (7). We concluded that CC treatment cannot elicit any pituitary-stimulatory or gonadotropin-like activities in sheep, and hence, cannot be applied in ewe breeding.…”