The role of luteal steroid hormones in the regulation of the estrous cycleof high fecundity Olkuska sheep

The study was undertaken to investigate the steroid hormone production by s heep luteal cells. Corpora lutea were collected from 30 Olkuska sheep on Da ys 3, 6, 9, 12 and 15 of the estrous cycle during the reproductive season. In Experiment 1, steroid hormone concentration was estimated in extracts of CL. In Experiment 2, luteal cells were cultured in vitro for 24 h. Luteal cells isolated on Days 9 and 12 secreted high amounts of progesterone and a ndrogens but smaller amounts of estradiol. Concentration of these steroids in CL extracts collected on the same days showed the same trend. In CL harv ested on Day 15, a decrease in androgens and progesterone as well as a sign ificant increase in estradiol were observed in culture media and in extract s. Judging from the high amounts of estradiol and low amounts of androgen o bserved at the end of the luteal phase, we speculate that the steroid hormo nes secreted by the regressing CL may play an active role in the regulation of the estrous cycle in the Olkuska sheep with autocrine influence on the luteal activity or a possible paracrine action on follicular growth. In the third Experiment, the possibility of heterogeneity in the multiple c orpora lutea population of prolific Olkuska sheep was investigated. Differe nces were found in the level of progesterone and estradiol secretion by ind ividual corpora lutea recovered from the same animal, which also varied in terms of weight. This is the first study which shows the existence of intra -ovarian and individual heterogeneity between corpora lutea recovered from ewes during the normal estrous cycle. (C) 2000 Elsevier Science B.V. All ri ghts reserved.