Histopathological and immunohistochemical findings during the sexual cycle in female mules and effects of long-term Regumate (R) administration

The aim of the first part of this study was a comparative immunohistochemical characterisation of the uterine secretary proteins uteroglobin (UG), uterocalin (UC), uteroferrin (UF) and of the calcium-binding protein calbindin (CAL) in the endometrium of clinically acyclic (n = 4) and "cyclic" mules (n = 2) considering clinical-gynaecological findings, endometrial functional morphology and blood serum concentrations of progesterone and estradiol. For this purpose a clinical-gynaecological examination was performed in five animals from April to August and in one mule until November 2004. Endometrial biopsies were taken concurrently (acyclic mules n = 46 biopsies, "cyclic" mules n = 51 biopsies). The endometrial proteins UG, UC, OF and CAL showed a very slight expression in the inactively differentiated endometria of the acyclic mules. In the endometria of the "cyclic" mules the secretion of these proteins was highly variable and no correlation between the phases of the sexual cycle, the concentration of the serum hormone values or the endometrial functional morphology could be detected. In the second part of the study two of the acyclic mules received an oral dose of 0.044 mg/kg BW (body weight) Regumate (R) for 50 days in order to examine the influence of a long-term progestin administration on the endometrial functional morphology. During the treatment period until 27 days post administration the mules were weekly biopsied and examined both gynaecologically and endocrinologically. Two years after the treatment endometrial biopsies were collected once more. The results obtained prior to Regumate (R) administration were compared with those during and after the treatment. On that account, 28 endometrial biopsies were examined pathohistologically (H. E. staining) and imunohistologically (UG, UC, UF, CAL, estrogen receptor (ER), progesterone receptor (PR), Ki-67 antigen). Prior to Regumate (R) medication the endometrium of the acyclic mule mares exhibited an irregular inactive differentiation with a very faint immunolabelling of all uterine proteins investigated. During the medication the endometrium developed a highly irregular secretary differentiation associated with a distinctly increased secretion of CAL, while the secretion of the other investigated proteins remained low. After cessation of the Regumate (R) administration as well as two years later the endometrium was found to be similarly irregular and inactive as before the treatment, the secretion pattern of the endometrial proteins was comparable to that before medication. In the course of the treatment an overall increased and highly variable expression of the steroid hormone receptors was noted. The administration of Regumate (R) did not show any significant influence on the endometrial proliferative activity. The results of this study clearly show that in mule mares an exogenous long-term administration of progestins causes an exceedingly pronounced secretary differentiation in the endometrium of acyclic mules, and beyond this generates distinctly visible and in principal reversible morphologic and functional alterations (maldifferentiations) as described in mares