Histologic, immunocytologic and subcellular changes in the rat adenohypophysis caused by prolactin, growth hormone and ACTH-producing transplanted pituitary tumors: A comparison with spontaneous prolactin-producing adenomas

Abstract

The effects of three transplanted pituitary adenomas on the intrasellar nontumorous adenohypophysis of rats hosting these tumors were investigated by histology, immunocytochemistry and electron microscopy. The first two tumors, designated MtT. W5 and MtT. W10 secreted prolactin and growth hormone, while the third, MtT. F4 produced prolactin and ACTH.

The intrasellar pituitaries appeared smaller, immunocytochemistry demonstrated a reduction in prolactin positivity in the anterior pituitaries of rats hosting MtT. W10 and MtT. F4 tumors. A similar reduction was noted for growth hormone in the adenohypophysis of rats bearing MtT. W5 and MtT. W10 tumor implants. Ultrastructural investigation revealed an apparent decrease in secretory granule size associated with a reduction in cell volume in the mammotrophs, somatotrophs and corticotrophs exposed to hypersecretion of their respective hormones. The number of cytoplasmic organelles appeared to be diminished. It was apparent that in rats with transplanted pituitary tumors, a feedback mechanism exists, altering the morphology of the respective nontumorous adenohypophysial cells and presumably inhibiting their secretory activity.

These changes were compared with a prolactin-secreting adenoma arising spontaneously in the pituitaries of aging Long-Evans rats. In these animals, the pituitaries were enlarged and the number of immunoreactive mammotrophs in the nontumorous portions of the adenohypophysis was markedly increased. The fine structural morphology of the nontumorous mammotrophs differed from those in the previous three groups, and was consistent with increased secretory activity similar to that found in normal lactating rats. These findings support the assumption that the morphologic features of these mammotrophs were not affected by prolactin secretion of the tumor.