FOLLICULAR GROWTH DURING THE NORMAL CYCLE AND AFTER TREATMENT WITH PROGESTAGENS IN THE EWE

Abstract

Follicular development in the ewe was studied during the normal estrous cycle and during and after treatment for 13 days with 6alpha-methyl-17alpha-acetoxy-progesterone (MAP). Estradiol-17beta concentrations in the liquor folliculi were also studied. During the estrous cycle growth waves were observed from Days 1 to 10 and from Days 6 to 17. Estradiol concentrations were low through Day 14 and reached maximum values on Day 16. The presence of 3beta- and 17beta-hydroxysteroid dehydrogenase (3beta HSD 17beta HSD) activities in the theca interna cells of follicles from Days 1 to 16 may explain the variations in the synthesis of estrogen. The administration of MPA prolonged follicular life. 3beta-HSD activity which was not observed in the membrane granulosa of follicles was detectable for at least 6 days in the membrane granulosa after treatment. MAP did not inhibit the growth of new follicles and only slightly inhibited follicular steroid synthesis. Rapid new follicular growth was evident after termination of MAP treatment. Some of these net follicles showed 3beta-HSD activity in the membrane granulosa and 17beta-HSD activity in the membrane granulosa and 17beta-HSD activity in the theca interna. This indicates that ovarian secretion of estrogens can occur in the 1st estrous cycle a fter discontinuation of treatment with progestogens. It is hypothesized that subfertility in the 1st estrus after treatment with progestagens may be due to insufficient suppression of follicular growth and steroid synthesis in the ovaries during treatment.