Immunohistochemical studies on S-100 cells in the anterior pituitary gland of Sprague Dawley rats and spontaneous dwarf rats.

The S-100 cells in the pituitary glands of adult male Sprague Dawley rats (SDs) and spontaneous dwarf rats (SDRs) were immunohistochemically examined using anti-S-100 alpha and anti-S-100 beta monoclonal antibodies. The immunoreactive cells against S-100 protein were divided into three subtypes on the basis of their immunoreactivity against subunits of S-100 protein: S-100 alpha dominant type (the alpha-type cell), S-100 beta dominant type (the beta-type cell) and immunoreactive against both S-100 alpha and S-100 beta (the alpha beta-type cell). In the SD, alpha-type cells represented 26% of the total S-100 immunoreactive cells (S-100 cells) and were localized in the peripheral area of the ventral region of the pituitary gland. This type of cell was observed forming clusters, with more abundant cytoplasm than the beta-type cell. The proportion of beta-type cells was 53%. They were diffusely distributed throughout the gland, and their processes were thicker than those of the alpha-type cell. In the SDR, the proportion of alpha-type cells was 55%, and they were observed throughout the gland. In contrast, beta-type cells totalled 12% and were localized in small areas of the central and peripheral region of the gland. The proportion of alpha beta-type cells was 21% in the SD and 33% in the SDR and they were observed forming small clusters in both animal groups. The proportion of alpha-type cells compared with the total of S-100-immunoreactive cells was significantly higher (P < 0.05) in the SDR than in the SD, while the proportion of beta-type cells was markedly lower (P < 0.05).