The aim of the present study was to examine the distribution of oestrogen receptor alpha (ERα) in the uterus of sows with reproductive disturbances as well as to study the expression of ERα in relation to plasma oestradiol-17β (E₂) and progesterone (P₄) concentrations in the blood. Crossbred 3–4 parity Lithuanian White x Danish Landrace breed sows presenting various reproductive disturbances were recruited for the present study. Immunohistochemical investigation of sows’ uterus horns was carried out by the streptavidin–biotino peroxidase method using antibodies against ERα. Blood samples were collected from the jugular vein 1 h prior to slaughter for analysis of E₂ and P₄ levels.
Examination revealed that ovaries in 78.3% of sows remained active during the supposed anoestrus. 5% of the sows with active ovaries, as it became evident after post-mortem examination, were in oestrus despite the fact that no visual signs of oestrus were observed before slaughtering. The ERα were distributed in all uterine tissue compartments: surface epithelium, subepithelial connective tissue, glandular epithelium and in muscle cells of the myometrium. The lowest number (<30%) and lowest staining intensity (+) of positively stained for ERα nuclei found in uterine wall compartments were observed at oestrus, though the E₂ concentration in blood was high (43.03 pmol/l). Glandular epithelial nuclei stained positively for ERα in >80% of cells at late dioestrus, but staining intensity differed through the rest of the oestrus cycle stages. The most prominent staining of ERα in the myometrial cells was found at pro-oestrus when E₂ was high (350.79 pmol/l) and P₄ was low (15.45 nmol/l), and at late dioestrus when the concentration of E₂ and P₄ was low (3.42 and 0.19 nmol/l, respectively). The concentration of P₄ was high (49.01 nmol/l) at dioestrus and low at late dioestrus, while the concentration of E₂ was low at both stages. The intensity of nuclear positive staining varied not only among the stages of the oestrus cycle, but also among the different uterine compartments.
In conclusion, we determined that sows with reproductive disturbances had cyclic active ovaries, but the levels of P₄ and E₂ in their plasma did not fully fit the physiological norm of these hormones during their oestrus cycle. Similarly, ERα expression in different uterine compartments of sows is the very low.
 

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