Relationship between LH receptor concentrations in thecal and granulosa cells and in-vivo and in-vitro steroid secretion by ovine follicles during the preovulatory period

Abstract

Summary. Ewes were ovariectomized before (Group 1, N = 5) or after (Group 2, N = 6) the peak of the preovulatory gonadotrophin surge. Ovarian secretion rates of oestradiol and testosterone were significantly higher in Group 1 than in Group 2. The presence of high levels of LH receptors in both thecal and granulosa cells was used to identify ovulatory from non-ovulatory follicles. There was a significant fall in the LH receptor concentration in the thecal and granulosa cells of ovulatory follicles after the peak of the preovulatory gonadotrophin surge. Ovulatory follicles in Group 1 produced significantly more oestradiol and testosterone in vitro than did those in Group 2. In both groups ovulatory follicles secreted significantly more oestradiol in vitro than did non-ovulatory follicles. Follicular fluid oestradiol concentrations were similar in pattern to the in-vitro oestradiol secretion activity in ovulatory and non-ovulatory follicles. However, follicular fluid testosterone concentrations were significantly higher in non-ovulatory follicles than in ovulatory follicles. Incubation of follicles with 250 ng testosterone/ml did not significantly alter the in-vitro oestradiol secretion rate in any of the groups of follicles except for Group 2 non-ovulatory follicles in which oestradiol accumulation increased. The number of thecal and granulosa cell LH receptors was significantly correlated with follicular fluid oestradiol concentrations in ovulatory follicles and with in-vitro oestradiol production by Group 1 ovulatory follicles. It is suggested that the fall in oestradiol secretion rates, which occurs after the peak of the preovulatory gonadotrophin surge, may be due to a decrease of aromatase activity associated with a fall in the concentration of LH receptors and is not due to a lack of the oestrogen precursor testosterone. The elevated concentration of testosterone and low oestradiol concentrations in non-ovulatory follicles compared with ovulatory follicles are probably due to an inactive aromatase system, perhaps associated with the lack of granulosa cell LH receptors.

Direct effect of prolactin, induced by TRH injection, on ovarian oestradiol secretion in the ewe

“…Normal secretion of oestradiol requires both the stimulation by LH of androgen production, principally androstenedione and testosterone, from the theca and its conversion to oestradiol by an active aromatase system induced by FSH and possibly LH in the granulosa cell layer of the follicle (Moor, 1977;Armstrong, Weiss, Selstam & Seamark, 1981;McNatty, Gibb, Dobson, Thurley & Findlay, 1981 (Dorrington & Gore-Langton, 1981) and LH-induced androgen production from ovarian thecal and interstitial cells in vitro (Magoffin & Erickson, 1982 (Carson, Findlay, Burger & Trounson, 1979;Webb & England, 1982). However, this seems unlikely as most studies of the rat indicate that prolactin is part of the hormonal complex necessary for the induction and maintenance of LH receptors in the follicle and corpus luteum (Richards & Williams, 1976;Holt, Richards, Midgley & Reichert, 1976).…”

Oocyte-Somatic Cell Interactions and Ovulation Rate: Effects on Oocyte Quality and Embryo Yield

“…overall, the total population of lh-receptive gc in the follicles in the BMp15 mutant is similar to that in the wild-type follicle(s). Follicles with lh-receptive gc are the putative ovulatory follicles, 59 and are the dominant ovarian sources of estradiol and inhibin. 54 since the major sources of these hormones are the gc, the total ovarian secretions do not differ between these genotypes and consequently the ovulation rate differences occur without any differences in the plasma concentrations of pituitary gonadotropins.…”

Alterations in follicular dynamics and steroidogenic abilities induced by heat stress during follicular recruitment in goats

“…More recently, Kanai et al (1995) found that heat stress did not change the pituitary LH secretion in long-day-treated anoestrous goats that were injected with exogenous gonadotrophin-releasing hormone (GnRH) to induce artificial LH pulses, whereas it reduced the follicular responsiveness to LH. Follicular LH responsiveness is attributed to the expression of LH receptors on the follicles (Webb & England 1982). Therefore, it appears probable that heat stress induces alterations in the follicular LH receptors.…”