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Title: Luteolysis in the mare : a role for the immune system and gonadotrophins?
Author: Lawler, Denise Fionnuala
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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We investigated the presence, and changes in numbers, of populations of inflammatory cells in the equine CL at different stages of the oestrous cycle, after exogenous PGF administration to artificially induced luteolysis, and in early pregnancy. As found in other species, populations of cells did vary with stage of the cycle, and the selective infiltration of cytotoxic T-cells identified prior to functional luteolysis may indicate a role for them in this process. Changes in MHC class II expression by luteal cells, which could potentially instigate an immune reaction, were not identified in our study. Investigation of the chemoattractant properties of luteal tissue taken at similar time-points, revealed that even by day 12-14 of the cycle leucocytes were attracted to the CL. This increased after functional luteolysis, especially with regard to mononuclear cells, while PGF-treated tissue expressed even greater attractant activity. The identity of the chemoattractants was not determined, although collagen or collagenases may play a minor role. Administration of GnRH analogues to cattle in dioestrus has been reported to prolong luteal function, and improve pregnancy rates to the preceding insemination. In attempting to create a model for prolonged luteal function in the mare, a GnRH analogue was administered, and endocrine and ovarian responses monitored. Treatment had no significant effect on oestrous cycle length, progesterone levels, or follicular dynamics. It did however significantly reduce oestradiol levels compared to control systems. This may reflect altered folliculogenesis, which, in turn, could affect luteolysis. This was not detected in our study, and therefore did not provide us with a model for prolonged luteal function. Treatment of mares with a GnRH antagonist during dioestrus has previously been found to attenuate progesterone levels, and cause premature luteolysis in treated animals, indicating a role for LH in supporting equine luteal function. We further investigated the role of gonadotrophins in equine luteal function by identifying and localising LH receptor mRNA expression in equine follicles and CL by in situ hybridisation. Expression was maintained in CL until functional luteolysis, after which it was considerably reduced. mRNA levels also remained high in CL or early pregnancy, while PGF treatment had varying results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available