Histological, hormonal and biomolecular analysis of the pathogenesis of ovine Prolapsus vaginae ante partum

The objectives of the present study were to evaluate the hormonal profiles, histology of the vagina and biomolecular analysis of connective tissue of ewes with and without vaginal prolapse. Blood samples from the jugular vein and biopsies of the vaginal tissue were taken from five late term pregnant, unaffected animals, four sheep during parturition and six ewes suffering from vaginal prolapse ante partum. The blood samples were submitted for determining the concentration of the steroid hormones progesterone by automatic luminescence immunoassay and estradiol-17β by the sequence test. Investigations in the mRNA-expression including the estimation of the transcript levels of the α₂-chain of collagen I, the collagenolytic metalloproteinase 1 (MMP 1), the tissue inhibitor of MMP 1 (TIMP 1) and the estrogen receptor α were carried out by using semiquantitative reverse transcription-PCR. Additionally, the histology of the vaginal wall of ewes with and without vaginal prolapse and animals intra partum was assessed. Because of a right-skewed distribution, data were logarithmised and described using the geometric mean (x̄g) and the dispersion factor (DF). The average progesterone concentration of affected ewes (x̄g = 19.35 ng/ml, DF 1.33) was above those of control animals ante (x̄g = 10.44 ng/ml, DF 1.58) and intra partum (x̄g = 9.24 ng/ml, DF 1.92). Compared to the pregnant control group (x̄g = 20.13 pg/ml, DF 1.49) the plasma levels of 17β-estradiol in animals suffering from ante partum vaginal prolapse (x̄g = 27.81 pg/ml, DF 1.56) appeared to be slightly increased, but the difference was without statistical significance. The analysis of mRNA expression revealed a difference in the ante partum collagen metabolism in affected sheep. In prolapsed tissue the α2-chain of collagen I showed a decreased expression level in relation to the control animals in late-term pregnancy (P < 0.01). The average mRNA synthesis of MMP 1 or TIMP 1 in affected ewes was higher or lower, respectively, than the synthesis in healthy, late-term pregnant sheep. Significant differences were not observed. The production of transcripts of the estrogen receptor α was significantly decreased within the group of affected sheep compared to the unaffected pregnant ewes. Histological assessment showed that oedema was only detected in the subepithelial zone of the vaginal wall of intra partum sheep. There was no evidence for an inflammation of the prolapsed vaginal tissue since infiltration of leucocytes was present in all samples equally. The thickest vaginal epithelium due to hyperplasia of the epithelial cells was observed in sheep suffering from ante partum vaginal prolapse (x̄g = 83.95 μm, DF 1.21). This difference was statistically significant between the ante (x̄g = 31.12 μm, DF 1.22) and intra partum groups (x̄g = 33.27 μm, DF 1.24). Peripheral concentrations of progesterone and estradiol-17β seem to have no influence on the occurrence of vaginal prolapse in ewes. Regarding histology of the vaginal wall in combination with the expression of local estrogen receptors, it was determined that there is neither a pronounced oedema nor an overexpression of the estrogen receptor α in affected animals, which means that no local estrogenic effect provokes the prolapse of vaginal tissue. The biomolecular analysis led to the new result, that ewes suffering from vaginal prolapse show alterations in the antepartal metabolism of vaginal connective tissue.