A Delayed Antagonistic Effect of Progesterone on the Estradiol-Induced Differentiation of the Oviductal Epithelium in Spayed Cats

A delayed antagonistic effect of progesterone on the estradiol-induced differentiation of the oviductal epithelium in spayed cats was investigated. 2 groups of cats were treated wtih silastic implants of progesterone (12 cm) and estradiol (.5 cm) as follows: Group A: progesterone (7 days) progesterone plus estradiol (14 days). Oviducts were collected and fixed for morphologic and cytomorphometric determinations. Mean plasma levels of estradiol in Groups A and B were 16.8 and 19.7 pg/ml respectively. Mean plasma levels of progesterone were 14.1 ng/ml in Group A and .3 ng/ml in Group B. After 2 days of estradiol treatment cells from both treatment groups showed identical patterns of mitosis and hypertrophy On Days 3-5 combined treatment had prevented further cell hypertrophy but ciliogenesis was evident in cells from both groups. By Day 7 combined treatment had somewhat reduced the number of ciliated cells in the fimbriae (Group A 46% Group B 67%) and more dramatically in the ampulla (22 and 63% respectively). By 14 days combined treatment had led to further atrophy and extensive deciliation. The nonciliated cells never became functional secretory cells in the presence of progesterone. These results suggest that in cats a period of estradiol-induced differentiation must occur before progesterone can antagonize the estradiol effect that progesterone antagonism develops gradually and that the rate at which progesterone antagonism develops differs from 1 region of the oviduct to another.