The endometrium of the gynaecologically healthy mare during oestrus : a clinical, morphological, chemical and immunological study

Subfertility in mares increases with age. Among the common clinical findings in subfertile mares are an accumulation of intrauterine fluid, increased sensitivity to intrauterine infections and endometrial fibrosis, all of which are typical symptoms of persistent endometritis. It is therefore essential to study the gynaecologically healthy mare endometrium in order to gain a better understanding of its defence mechanisms. The aim of the research described in the present thesis was to study parameters of importance for the normal function of the equine endometrium during oestrus, in mares of various ages and parities. Special emphasis was placed on studying the formation of the intraluminal uterine fluid. In addition, the content of immunoglobulins in the intraluminal fluid and the occurrence and distribution of T-cells in the endometrium were determined.A total of 92 mares, Warmblood, Standardbred and Finnish breeds, were examined once during oestrus. The gynaecological examination included palpation ofthe genital organs, ultrasonography, vaginoscopy, cytological and bacteriological sampling of the endometrial surface, and the collection of undiluted uterine fluid. In addition, a videoendoscopical examination of the uterine mucosa was made, in connection with which small endometrial tissue samples were sampled for biopsy from visually selected areas. Based on the anamnesis together with the clinical examination and analyses ofthe collected samples, the mares that could be categorised as gynaecologically healthy were included in the studied population, 53 mares in total.The fine structure of the secretory endometrium was studied at the light and electron microscopical levels. A distinct oedema ofthe lamina propria was evident. The glandular epithelium presented clear signs of secretory activity with pronounced secretory vesicles containing electron-dense granula in the ad-luminal cytoplasm and a well-developed supranuclear Golgi apparatus. Secretory products and cell debris were commonly found in the gland lumen. X-ray microanalysis was performed on frozen endometrial tissue samples and microdroplets of intraluminal fluid and serum. Concentrations of selected elements (Na, K, Cl, S, P and Ca) were analysed in secretory vesicles in endometrial gland epithelium and compared with concentrations in undiluted uterine fluid and in serum. The elemental concentrations in undiluted uterine fluid were similar to those measured in serum, whereas the concentrations of elements in the secretory vesicles differed sharply from those in both uterine fluid and serum. The protein profiles (SDSPAGE) and concentrations oftotal protein, albumin and immunoglobulins A and G were determined in both undiluted uterine fluid and serum. There was a clear similarity between the protein profiles of uterine fluid and those of serum. Concentrations of total protein and albumin in uterine fluid were 52-56 % of those in serum. The concentration of immunoglobulin (Ig) A in undiluted uterine fluid was similar to its concentration in serum, whereas the concentration of IgG was approximately 45 % as high as its concentration in serum. The distribution and number of MHC class II, CD4 and CD8 expressing cells during oestrus in different segments of the endometrium were studied using immunohistochemistry. The three cell subsets were detected in all studied endometrial samples, with numbers of all three being higher in the uterine body than in the horn.In conclusion, during oestrus, the gynaecologically healthy equine endometrium is oedematous, and the uterine glands show intense secretory activity. Both the elemental composition and the protein profile of undiluted uterine fluid resembled the corresponding composition/profile of serum, thereby leading to the conclusion that the cyclical accumulation of uterine fluid during oestrus to a great extent is a transudate which is likely to have a diluting effect upon the specific secretion ofthe glands. Age had no influence on any ofthe studied chemical or immunological parameters.