Immunohistochemical localization of S-100 protein in the pig pituitary gland.

Immunohistochemical localization of S-100 protein was studied in anterior, intermediate and posterior lobe of the pig pituitary gland. Two immunopositive cells for S-100 protein were identified: the folliculo-stellate cells (FSc) in the glandular lobes and the pituicytes in the neural lobe. In the anterior lobe, immunoreactive folliculo-stellate cells were scattered among secretory cells. In the area where the secretory cells form strands and follicle-like groups the positive cells were concentrated in groups. In the intermediate lobe, S-100 protein-positive cells were located sparsely among secretory cells and next to secretory follicles and the pituitary cleft. These FSc were more voluminous and displayed fewer cytoplasmic processes. In the neurohypophysis, positive reaction for S-100 protein was seen in the pituicytes. These cells were distributed singly or concentrated in groups. The distribution, and morphologic characteristics of the FSc in the glandular lobes and the pituicytes in the neural lobe in the pig indicate different origin of both S-100 protein-positive cells.