Follicular growth and regression during the 8 days after hypophysectomy in sheep

Abstract

Ewes were hypophysectomized on Day 0 and ovariectomized 1, 2, 4 or 8 days later. There was no effect of hypophysectomy on the overall population of follicles greater than 0.8 mm in diameter during the time studied. However, the growth of healthy follicles greater than 2 mm in diameter was prevented by Day 2. Turnover of follicles was very active in the ovaries of hypophysectomized ewes as shown by peaks in the proportion of follicles in early atresia at Day 4 and in advanced atresia at Days 1 and 8. By Day 8, most of the measures of the population of follicles 0.8 to 2 mm in diameter were back to the values of Day 0 ewes. The mitotic index of the granulosa cells of the healthy follicles exhibited a similar pattern with a nadir at Day 2 followed by a return at Days 4 and 8 to values similar to Day 0 ewes. Ink-marked preovulatory follicles underwent a steady decrease in their histological size after hypophysectomy and this was associated with time-related changes in the health status of these follicles. By Day 1, 4 out of 7 follicles were still healthy while at Days 2, 4 and 8, all follicles were in advanced, late and collapsing atresia respectively. There was no evidence of an ability of PMSG (1000 i.u.) to rescue large follicles in advanced atresia (48 h after hypophysectomy). Furthermore, at 24 h after hypophysectomy, only 2 out of 5 follicles were maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian features contributing to the variability of PMSG-induced ovulation rate in sheep

“…The fact that the value of the correlation linking healthy follicles 0-8-20 mm in diameter and ovulation rate is actually decreased when atretic follicles are taken into account strongly suggests that they are not a component of the ovarian response to PMSG. The discrepancy between this finding and previous claims of follicular rescue from atresia by PMSG (Byskov, 1979;Peters, 1979;Monniaux et al 1984) could be explained by the observation that there were very few follicles in early atresia (about 6%) in this class and that PMSG does not rescue follicles in advanced atresia (Driancourt et al, 1987). In contrast to healthy follicles 0-8-2-0 mm in diameter which form the reserve from which PMSG recruits follicles for ovulation, the number of follicles >2mm in diameter was negatively correlated with PMSG-induced ovulation rate (r = -0-29 and -0-61 in Exps 1 and 2 respectively).…”

Single-chain human gonadotropin analogs induce follicle development in sheep

“…As in other species (Richards 1980), E 2 synthesis in sheep requires input from both the thecal and granulosa cells (Baird 1977, 1983, England et al 1981. The essential role of the gonadotropins in ovarian function is illustrated by the arrest offollicle development and E 2 synthesis in mature ewes made deficient in the gonadotropins by hypophysectomy (Draincourt et al 1987), hypothalamopituitary disconnection (Hudson et al 1999), immunoneutralization of endogenous GnRH (McNeilly et al 1986), or administration of long-lived GnRH agonists (McNeilly & Fraser 1987) or antagonists (Campbell et al 1998). Moreover, follicle development and E 2 synthesis are reinstated in gonadotropin-deficient sheep by administration of LH and FSH (Campbell et al 1998).…”

Effects of gonadotrophin deprivation on follicular growth in gilts

“…Hypophysectomy was conducted using the technique described by Du Mesnil du Buisson et al (1964 Driancourt et al (1987). Terminal stages of atresia where antrum is invaded by fibroblasts were not taken into consideration.…”