Preovulatory follicular development in sheep treated with PMSG and/or prostaglandin

Publisher Website
Google Scholar
Abstract
The patterns of growth and atresia of antral follicles including that of the presumptive preovulatory follicle were examined in sheep ovaries for a 24-48 h period after the induction of luteolysis with a prostaglandin analog, cloprostenol or cloprostenol + PMSG [pregnant mare serum gonadotropin]. Ewes were ovariectomized at various times after the initiation of the treatments. All follicles .gtoreq. 1 mm in diameter were dissected from the excised ovaries and the antral fluid and granulosa cells recovered. Individual follicles were classified as healthy or atretic on the basis of the number of granulosa cells recovered and then subclassified as to whether they contained intrafollicular levels of estradiol that were .gtoreq. or < 100 ng/ml. In another series of similarly treated ewes, the ovarian secretion rates of estradiol and the intrafollicular concentrations of estradiol in all large antral follicles (.gtoreq. 5 mm diameter) and the levels of progesterone in peripheral plasma were measured at different times after induction of luteolysis. A large estrogenic follicle (.gtoreq. 5 mm diameter and secreting .gtoreq. 1 ng estradiol/min) appears around 10 h after the cloprostenol injection and this presumptive preovulatory follicle emerges before the corpus luteum has ceased to function. Moreover, the presumptive preovulatory (estrogenic) follicle appears to develop from the pool of small estrogenic follicles (1-3 mm diameter) after the onset of luteolysis. The emergence of a large estrogenic follicle is accompanied by a widespread increase in atresia (> 80%) in all other classes of antral follicles (.gtoreq. 1 mm in diameter). During the first 10 h of cloprostenol-induced luteolysis, PMSG prevented the normal occurrence of atresia in the large follicle population; enhanced estrogen secretion in a greater proportion of large antral follicles compared to that in control animals; temporarily rescued and/or prevented small antral follicles (1-4 mm diameter) from undergoing atresia; but had little, or no, effect on the overall population of antral follicles (.gtoreq. 1 mm diameter). After 24 h, the atresia-preventing effects of PMSG were no longer discernible and the only obvious difference noted, compared to the controls, was the number of large estrogen-secreting follicles.

This publication has 16 references indexed in Scilit: