Immunolocalization of estrogen and progesterone receptors in ewe mammary glands

Immunopresence of estrogen receptor a (ERa), b (ERb) and progesterone receptor (PR) were examined in the ewe mammary gland from prepubertal stage to involution. Immunolocalization of ERa revealed a strong positive staining in nuclei of cells composing terminal ductular units (TDUs) in prepubertal ewes. A mild immunoreactivity was identified in early lactating gland. During late lactation immunoreactive product to ERa was observed in the cytoplasm of glandular epithelial cells in all alveoli. In mammary glands at involution ERa positivity was clearly nuclear, with weak to moderate cytoplasmic staining. Cytoplasmic strong immunostaining for ERb was detected in cells of TDUs, whereas some stromal cells exhibited nuclear staining. A nuclear ERb immunostaining was observed at early lactation, instead during late lactation, the positivity for ERb showed only a moderate cytoplasmic distribution. At involution, ERb positivity was very moderate and detected just in the cytoplasm of shrunken alveoli. Scattered nuclear staining of PR was observed just in mammary glands at early lactation. These results showed that in the mammary glands of sheep both estrogen receptor isoforms were displayed during lactation cycle and that PR appeared just at early lactation, reflecting their regulatory role in alveolar cells.