Corpora lutea induced by gonadotrophin-releasing hormone treatment of anoestrous Welsh Mountain ewes: reduced sensitivity to luteinizing hormone in vivo and to chorionic gonadotrophin in vitro

Abstract

Seasonally anoestrous Welsh Mountain ewes received 250 ng gonadotrophin-releasing hormone (GnRH) every 2 h, with (Group 1;n= 13) or without (Group 2;n= 14) progesterone priming for 48 h. Fourteen control ewes (Group 3) were studied during the luteal phase in the breeding season. Animals in Group 4 (n= 12) received progesterone priming followed by 250 ng GnRH at increasing frequency for 72 h, while ewes in Group 5 (n= 13) were given three bolus injections of 30 μg GnRH at 90-min intervals. All treatment regimens induced ovulation. However, only corpora lutea (CL) from ewes in Group 3 (breeding season) or Group 4 exhibited normal luteal function. Luteal luteinizing hormone (LH) receptor levels were significantly higher on day 12 than day 4, and CL from groups with adequate CL (3 and 4) had significantly higher125I-human chorionic gonadotrophin (hCG)-binding levels than the three groups with inadequate CL on day 12. LH-binding affinity was unchanged. Exogenous ovine LH (10 μg)in vivoon days 3 or 11 after ovulation induced a pulse of progesterone in ewes with adequate CL: however, ewes in Groups 1, 2 and 5 showed no significant response. Basal progesterone secretionin vitrowas significantly greater on day 4 than on day 12. Maximal steroidogenic responses of adequate and inadequate CL to hCG and to dibutyryl cyclic-3′,5′-AMP were similar at both stages of the luteal phase. However, the EC50for hCG on days 4 and 12 was 10-fold lower for groups with an adequate CL (0.1 IU hCG/ml) than for inadequate-CL groups (1 IU hCG/ml;P<0.05). Thus, in addition to the well-characterized premature sensitivity of GnRH-induced inadequate CL to endometrial luteolysin, we have shown (1) a marked decrease in total number of cells in the CL, a profound reduction in vascular surface area, and a decrease in mean large luteal cell volume (with no change in large luteal cell numbers), (2) decreased luteal LH receptor and progesterone content compared with adequate CL and (3) that CL that were becoming, or were destined to become, inadequate failed to respond to ovine LHin vivoand were 10-fold less sensitive to hCG in terms of luteal progesterone secretionin vitro.

Reduced LH sensitivity in vivo and in vitro of corpora lutea induced during anoestrus by GnRH, and during the late breeding season, in Scottish Blackface ewes

“…Thus, if we vary the treatment regimens (for example, with or without progesterone pretreatment and/or with different patterns of GnRH injection), anoestrous ewes ovulate in response to GnRH to form CL that are predominantly adequate (with (+) progesterone priming; luteal phase plasma progesterone concentrations of >1 ng/ml on 3 consecutive days) (Hunter 1991) or inadequate (without (-) progesterone priming; luteal phase plasma progesterone concentrations failed to achieve 1 ng/ml on 3 consecutive days). Interestingly, we showed in an earlier study in Welsh Mountain ewes that CL likely to become inadequate could be distinguished from those likely to become adequate as early as day 3 after ovulation, because of their failure to respond to a bolus of 10 µg oLH in vivo with a rise in plasma progesterone and their reduced sensitivity to hCG in vitro (Bramley et al, 2005). However, we found no effect of progesterone pretreatment alone on the frequency of adequate luteal phases.…”

“…Serum progesterone concentrations were measured by radioimmunoassay (Scaramuzzi & Baird 1974), as described previously (Bramley et al, 2005). Incubation medium did not interfere with the assay; therefore, the progesterone content of media was measured without solvent extraction.…”

“…Unoccupied LH receptor levels were measured by specific binding of LH receptor occupancy was measured by acid dissociation of bound oLH from triplicate aliquots (100 µl) of luteal homogenate with ice-cold 0·1 M citrate buffer, pH 3·0, as described previously (Bramley et al, 2005). for publication).…”

Male-induced short oestrous and ovarian cycles in sheep and goats: a working hypothesis

“…The hypothesis of a seasonal difference in follicular composition is not supported by the results of Cahill et al [28,29] who did not find any difference in granulosa cell content of the follicle of the breeding season compared to the anoestrous season. On the contrary, the hypothesis of a difference in the evolution of the luteal cells between D0 and D4 is supported by the description of an inadequate luteal function due to poor response to the LH surge during the final maturation of the anoestrous follicle in ewes [30,32]. In rats and women, if intrafollicular concentration of P4 is low, luteal development is abnormal [33].…”

Expression and localization of bone morphogenetic protein6 (BMP6) in the corpus luteum during different stages of estrous cycle in the buffalo (Bubalus bubalis)

“…These local factors include Transforming growth factor-β (TGF-β),Vascular endothelial growth factor (VEGF), Insulin-like growth factor (IGF), Fibroblast growth factor (FGF), Epidermal Growth Factor (EGF) and angiopoietin etc. (Ferrara et al, 2003;Kaczmarek et al, 2005;Bramley et al, 2005;Otrock et al, 2007). Among the ovarian factors, members of the TGF-β super family have a biological role in the folliculogenesis in the cow (Knight & Glister, 2006;Glister et al, 2010).…”