Some biological activities of cronolone and medroxyprogesterone acetate in the uterus of the sheep, mouse and rabbit.

Cronolone (9 alpha-fluoro-11 beta-hydroxy-17 alpha-acetoxypregn-4-ene-3,20-dione) is widely employed to regulate breeding activity in the ewe, but its biological activity in the uterus of this and most other species has not been studied. In this study several in vivo uterus-related activities of cronolone have been examined in the sheep, mouse and rabbit. In some experiments the corresponding activities of medroxyprogesterone acetate (6 alpha-methyl-17 alpha-acetoxypregn-4-ene-3,20-dione, MAP) were also examined. Cronolone maintained pregnancy in ovariectomized ewes but not in ovariectomized mice and rabbits; it terminated pregnancy in some mice and in all rabbits that were receiving daily progesterone treatment. Cronolone could not sensitize the mouse uterus for the induction of the decidual-cell reaction or block the induction of such sensitivity by progesterone, but did support limited growth of the oil-stimulated horn after sensitization with progesterone. Cronolone induced uteroglobin secretion by rabbit endometrium. It was concluded that, whereas MAP is a potent progestogen in the sheep, mouse and rabbit, cronolone is a progestogen in the sheep and rabbit only. In the mouse and especially the rabbit, cronolone has other, non-progestational activities, which block pregnancy.