Action of PMSG on follicular populations in the heifer

Abstract

The short-term action of PMSG on the population of growing follicles in cattle was studied using histological methods. On Day 7 of a synchronized oestrous cycle 10 Friesian heifers were unilaterally ovariectomized. The remaining ovary was immediately stimulated by an injection of PMSG (2000 i.u.) and was removed 48 h after the preovulatory discharge of LH. Control animals did not receive any injection of PMSG. In all ovaries, follicles greater than 70 micron diameter were counted, measured and checked for atresia. The mitotic index in granulosa cells of follicles of different sizes was estimated in both ovaries of all the PMSG-injected animals. Unilateral ovariectomy alone had no significant effect on follicular populations. In the interval between PMSG injection and removal of the second ovary (148 +/- 22.7 h), PMSG significantly increased the number of normal preantral follicles but did not change the number of normal antral follicles. The mitotic index doubled in preantral and early antral follicles but remained unchanged in large antral follicles. PMSG stimulated slightly the growth of the antrum in large antral follicles but did not stimulate its formation in preantral follicles. The incidence of atresia among antral follicles, particularly the largest ones (diam. greater than 1.7 mm), was significantly reduced after PMSG, suggesting some 'rescue' of follicles from atresia.

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).…”

Ovarian follicular development during early pregnancy in cattle

“…The high variability in the population of antral follicles amongst cows was in the range of that reported previously (Erickson, 1966;Monniaux, Chupín & Saumande, 1983;Monniaux, Mariana & Gibson, 1984;Dufour & Roy, 1985). There were about 8-9 times more non-atretic than atretic follicles in the ovary of each animal and the number of these two types of follicles was positively correlated (r = 0-78).…”

“…Secondly, pregnancy was associated with an increased level of atresia in larger classes of follicles. Factors such as gonadotrophin concentration (Dufour, Cahill & Mauleon, 1979;Monniaux et al, 1983Monniaux et al, , 1984, season (Dufour & Guilbault, 1984), level of nutrition (Maurasse, Matton & Dufour, 1985), breed (Driancourt, Cahill & Bindon, 1985) and post-partum interval (Dufour & Roy, 1985) also altered the close equilibrium amongst follicular size classes in ewes and cows. The results of the present study therefore suggest that pregnancy induces a more rapid turnover of follicles from class 1 to classes 3 and 4 but may limit further follicular growth by increasing the degree of atresia in larger size classes.…”

A Simple Superovulation Method of A Single Injection of Follicle-Stimulating Hormone Combined with Equine Chorionic Gonadotropin for Superovulation of Suffolk Ewes During the Breeding Season: I. Effects of Different Treatments on the Endocrine Profiles.

“…FSH appeared to play a main role in the recruitment of follicles in the group of potentially ovulatory follicles by increasing aromatase activity [22]. ECG may not only increase the number of follicles due to its FSH-like activity, but also prevent the process of atresia [23] and can contribute to the production of more maturing follicles and to a greater production of E 2 by increasing production of androgen in the theca cells by its rather strong LH-like activity [24]. ECG can also help to prolong the stimulation to follicles by its long half-life.…”