Double-labeling immunogold electron-microscopic study of hormonal colocalization in nontumorous and adenomatous rat pituitaries.

According to the one cell, one hormone theory, the pituitary gland is composed of 5 cell types which secrete 6 hormones. Recent investigations indicate that this theory must be modified, as there are some bihormonal cells containing 2 hormones, i.e., mammosomatotrophs prolactin-growth hormone (PRL-GH). This study was undertaken in order to elucidate whether other adenohypophysial cells are capable of producing 2 hormones and to demonstrate the presence of cells coexpressing PRL-GH, PRL-thyrotropin (TSH), or TSH-GH. Sixteen nontumorous and 16 adenomatous male and female Sprague-Dawley and Long Evans rat pituitaries were removed immediately after the animals were killed and processed for transmission electron microscopy and the immunogold double-labeling technique. Coexpression of PRL-GH, PRL-TSH, and TSH-GH was found in both nontumorous and adenomatous pituitaries. Double labeling was present not only in the same cell cytoplasm but also in the same secretory granules. The question of whether these double-labeled cells represent different cell populations, transitional cell types, or precursor cells requires further investigation.