Immunocytochemical localization of oxytocin in corpora lutea and luteinized cysts from anoestrous ewes stimulated with gonadotrophin-releasing hormone

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

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.

Follicle development in cyclic, anoestrous and FSH-treated brushtail possums (Trichosurus vulpecula)

The common brushtail possum (Trichosurus vulpecula) is a pest of considerable economic importance in New Zealand. Attempts to develop methods of suppressing reproduction in this species are currently hampered by the lack of reliable methods to synchronise oestrus and ovulation in this species. The objective of this study was to compare antral follicle populations in anoestrous and cyclic brushtail possums and to assess the efficacy of exogenous FSH to induce follicle development in anoestrous animals. Ovaries were recovered from anoestrous possums after administration of either exogenous FSH (1.0 mg/injection) or the saline vehicle alone (0.5 ml/injection) at 12-h intervals for 3 days (n = 6/group), and from cyclic animals (n = 6) that were euthanised in mid-follicular phase (5 days after removal of their pouch young). All antral follicles > or =1.0 mm in diameter were dissected free of extraneous tissue, incubated in vitro to measure oestradiol production, and then processed for histological assessment of health status. Mean weight of ovaries and vaginal cul-de-sac tissues were both significantly greater (P<0.001) in FSH-treated anoestrous females (24.2+/-5.1 mg and 6.50+/-1.34 g, respectively), but did not differ significantly between saline-treated anoestrous possums (12.4+/-3.0 mg and 1.31+/-0.27 g) and cyclic animals (13.5+/-1.6 mg and 2.62+/-0.95 g). Mean uterine weights in both cyclic (889+/-161 mg) and FSH-treated (1098+/-184 mg) animals were significantly heavier(P<0.001) than those of anoestrous possums (414+/-61 mg). The mean number of follicles (> or =1.0-mm diameter) present was significantly greater (P<0.001) in FSH-treated, than in cyclic and anoestrous possums (38.0+/-4.4, 23.2+/-3.2 and 10.7+/-3.4 follicles/animal, respectively). Cyclic animals had significantly more (P<0.01) follicles than anoestrous possums. The proportion of follicles that were classified as healthy, was significantly lower (P<0.01) in cyclic possums(38%) than in anoestrous (69%) and FSH-treated (88%) animals. The mean diameter of the largest healthy follicle present was 2.5+/-0.41, 2.1+/-0.08, and 3.1+/-0.15 mm for cyclic, anoestrous and FSH-treated animals, respectively. None of the follicles harvested from saline-treated anoestrous possums produced measurable levels of oestradiol in vitro, whereas 7% and 59% of those from cyclic and FSH-treated animals did so. In summary, cyclic possums had more antral follicles present than anoestrous animals, but a lower percentage of these follicles were healthy. Less than 10% of healthy follicles from cyclic possums, and none of those from anoestrous animals, were capable of producing oestradiol when incubated in vitro. Treatment with ovine FSH promoted follicle development in anoestrous possums, to significantly increase the number of follicles present, the proportion that were healthy and the percentage capable of producing oestradiol.