Abstract
Inguinal mammary tissues from each of 3 male and 2 diestrous female rats of both Sprague-Dawley (SD) and Fischer 344 (F344) strains were harvested 30 min after an i.p. injection of bromodeoxyuridine (BrdU) at the ages of 3, 5, 7, 11, 15, and 19 weeks, respectively, examined using whole mount preparations, histologic methods, and histochemical techniques for BrdU, actin and peanut agglutinin (PNA) binding capacity, and compared with the same age and strain specimens of the opposite sex or with each of 13 castrated males of both strains. In SD males aged 7 weeks and F344 males aged 11 weeks, the mammary glands became more florid than in females. A striking predominance was noted in the duct-lobular system of adult male rats, in which many clusters of large, contiguous cuboidal cells exhibiting neither obvious lobuloalveolar orientation nor distinct lumen were observed. The clusters contained many myoepithelial cells in peripheral portions, and their epithelial cells manifested less BrdU labeling, more PNA binding capacity, and moderately fatty change. These findings were confirmed ultrastructurally in the clusters of 22-week-old male rats of both strains. Such a “male type” was more prominent in adult SD than in adult F344 strains. It could not be detected in either strains 4-8 weeks after orchiectomy performed before or after puberty. Therefore, these clusters would not have resulted from proliferating gland cells, rather from severe hypertrophy in ductulus luminal cells, and this sexual dimorphism may depend on sex hormones and strain difference may be related partly to maturation.
