Ovarian responses in gonadotrophin-releasing hormone-treated anoestrous ewes: follicular and endocrine correlates with luteal outcome

Abstract

The relationships between the development of antral follicles (growing from 3 to > or = 5 mm diameter), hormone secretion (luteinizing hormone (LH), follicle-stimlating hormone (FSH), oestradiol and progesterone), ovulation and the formation of luteal structures in response to gonadotrophin-releasing hormone (GnRH) were examined in 24 anoestrous Western White Face ewes (May-July). Ewes were monitored by transrectal ovarian ultrasonography for 34 days, commencing 15 days before the administration of GnRH. Following treatment with GnRH, 83% (20/24) of ewes ovulated. Twenty-five per cent of all ewes (6/24) subsequently had normal (full-life span) corpora lutea (CL), 37% (9/24) had inadequate CL, 17% (4/24) had both normal and inadequate CL, 17% (including three of four anovular ewes and one ewe with inadequate CL) formed luteinized follicles and only 4% (1/24) did not ovulate or produce any luteal structure. None of the variables of follicular growth (follicles reaching > or = 5 mm diameter) differed between follicles that either ovulated or failed to ovulate and there was no evident correlation between the age or stage of development of ovulatory sized antral follicles and the type of luteal structure formed, except for luteinized unovulated follicles; these follicles all emerged within 3 days of GnRH injection. Mean serum concentrations of FSH and oestradiol before treatment did not differ (P>0.05) between ewes with different ovarian responses, but peaks of fluctuations in serum concentrations of FSH in daily samples were higher in ewes that produced normal CL compared with ewes with inadequate CL. After GnRH treatment, oestradiol secretion was higher in ewes that formed luteinized unovulated follicles than in all ewes with inadequate CL (P<0.05). The peak concentration of the GnRH-induced LH surge was higher and the interval from GnRH to peak LH discharge was shorter in ewes with inadequate CL compared with ewes that had normal CL after ovulation (P<0.05). In conclusion, ovulatory sized antral follicles at a similar stage of their life span can give rise to either normal or inadequate CL and a proportion of these follicles do not ovulate in response to GnRH in seasonally anoestrous ewes. This suggests differences in ovarian follicular responsiveness to gonadotrophic stimuli. Both the amplitude of episodic elevations in daily serum FSH concentrations and the characteristics of the pre-ovulatory LH surge may be important for luteogenesis following ovulation.

Ovarian and Hormonal Responses to Follicular Phase Administration of Investigational Metastin/Kisspeptin Analog, TAK‐683, in Goats

“…In the present study, the ovulatory follicles in the treatment group emerged after TAK-683 treatment, and they were smaller in maximal diameter than those in the control group, suggesting that TAK-683 treatment results in follicular turnover and developing follicles ovulate prior to sufficient maturation. Previous studies demonstrated that GnRH-induced ovulation of premature follicles results in luteal dysfunction after ovulation in ewes (Bartlewski et al 2001). Although the direct mechanism of action of kisspeptin and TAK-683 on follicular and luteal cells is still unclear, reduced progesterone concentrations in the treatment group may have been involved in the interaction between the timing of ovulation and follicular maturation, modulated by TAK-683 treatment.…”

“…Previous studies demonstrated that GnRH‐induced ovulation of premature follicles results in luteal dysfunction after ovulation in ewes (Bartlewski et al. ). Although the direct mechanism of action of kisspeptin and TAK‐683 on follicular and luteal cells is still unclear, reduced progesterone concentrations in the treatment group may have been involved in the interaction between the timing of ovulation and follicular maturation, modulated by TAK‐683 treatment.…”

Ovarian Responses, Hormonal Profiles and Embryo Yields in Anoestrous Ewes Superovulated with Folltropin®‐V after Pretreatment with Medroxyprogesterone Acetate‐releasing Vaginal Sponges and a Single Dose of Oestradiol‐17β

“…Variations in the preovulatory LH surge (Veiga‐Lopez et al. 2006) and/or follicular responsiveness to gonadotropic hormones (Bartlewski et al. 2001) could both contribute to the failure of ovulation of some large antral follicles as well as reduction in the number of luteinized unovulated follicles in E 2 ‐17 β ‐treated ewes.…”

“…Variations in the preovulatory LH surge (Veiga-Lopez et al 2006) and/or follicular responsiveness to gonadotropic hormones (Bartlewski et al 2001) could both contribute to the failure of ovulation of some large antral follicles as well as reduction in the number of luteinized unovulated follicles in E 2 -17b-treated ewes. Luteinizing hormone plays a key role in the control of ovulation and luteogenesis (Baird 1992) and FSH and oestradiol stimulate the synthesis of LH receptors in preovulatory follicles (England et al 1981).…”

Progesterone improves the maturation of male-induced preovulatory follicles in anoestrous ewes

“…In addition, it is now well known that male-induced short cycles are not associated with premature LH surges (Pearce et al 1987). However, insufficient secretion of LH and FSH remains an obvious hypothesis to explain poor follicular quality during seasonal anoestrus (Bartlewski et al 2001).…”