Relationship between morphological development and sex hormone receptor expression of mammary glands with age in male rats

Abstract

The aim of this study is to investigate the changes with age on morphology and sex hormone receptor expression in the mammary glands of male Sprague-Dawley rats, focusing on male-specific cells, "oxyphilic cells", observed after sexual maturity. The mammary glands of male rats at 14, 21, 35, 50, 75 and 100 days old were examined by gross observation, microscopic observation using whole mount specimens, histological and immunohistochemical sections. Grossly, mammary glands showed brown color at 50-100 days old. In whole mount specimens, terminal end buds (TEBs) were observed at 14-50 days old and the number of TEBs was highest at 35 days old. Histologically, the male mammary glands contained small epithelial cells with scanty cytoplasm at 14-35 days old while ductal and lobular epithelial cells were changed into oxyphilic cells with abundant cytoplasm at 50-100 days old. Immunohistochemicaly, androgen receptor (AR), estrogen receptor (ER) and progesterone receptor (PgR) expressions were found in both mammary glands found at a young age and oxyphilic cells. In oxyphilic cells, AR expression was dominant compared to ER and PgR expressions and increased with age. From these results, the development at 50-100 days old might be strongly related to AR. Ultrastructural observation of oxyphilic cells confirmed a number of lipid droplets, deformed and/or enlarged mitochondria, lysosomes and peroxisomes in their cytoplasm.

Keywords: development; hormone receptor; male rat; mammary gland; oxyphilic cell.

Fig. 1.

Gross examination. Right mammary glands in male rats at 14 (a, b), 21 (c, d), 35 (e), 50 (f, g), 75 (h, i) and 100 days old (j). Brown mammary glands were observed at 50–100 days old (f–j).

Fig. 2.

Whole mount specimen. Morphological changes of the mammary glands in male rats at 14 (a), 21 (b), 35 (c), 50 (d), 75 (e) and 100 days old (f). TEB: terminal end bud, AB: alveolar bud, LOB: lobule, Du: duct. Scale bars, 500 µm.

Fig. 3.

Histological examination of the mammary glands in male rats at 14 (a), 21 (b), 35 (c) and 50 days old (d-f) (H&E stain). At 50 days old, both structures with morphology at a young age (d) and oxyphilic cells (e) were observed. (f) is the enlarged figure of structure with oxyphilic cells. TEB: terminal end bud, AB: alveolar bud, Du: duct. Scale bars, 100 µm (a–e), 50 µm (f).

Fig. 4.

Histological examination of the mammary glands in male rats at 75 (a, b) and 100 days old (c–f) (H&E stain). (e) and (f) are the enlarged figures of a lobule consisted of oxyphilic cells. Du (y): duct with morphology at a young age, Du (oxy): duct consisted of oxyphilic cells, LOB (oxy): lobule consisted of oxyphilic cells, Scale Bars, 100 µm (a–d), 50 µm (e), 25 µm (f).

Fig. 5.

Immunohistochemical examination of the mammary glands in male rats. In the mammary gland at 35 days old (a, c, e), androgen receptor (AR) expression was not found (a) while estrogen receptor (ER) expression was found (c, arrows). Progesterone receptor (PgR) expression was observed in a small number of cells. The inset of (e) shows a PgR positive cell (arrow). In the oxyphilic cells at 100 days old (b, d, f), the portion of AR expression was high while the portions of ER and PgR were low. (a, b) AR, (c, d) ER, (e, f) PgR. Scale Bars, 25 µm.

Fig. 6.

Transmission electron microscopic examination of oxyphilic cells of the mammary glands in male rats at 75 days old. Small lumen with microvilli was found (b, arrowhead). N: nucleus, G: Golgi apparatus, rER: rough-surfaced endoplasmic reticulum, Ly: lysosome, P: peroxisome, M: mitochondria, Li: lipid drop. Scale bars, 1 µm.