Ultrastructural characteristics of TSH-producing adenomas with special reference to its close similarity to BFA-treated pituitary adenoma cells.

Two of 420 patients with pituitary adenoma who underwent operation from 1989 to 1997 had thyroid stimulating hormone (TSH) producing adenoma. We investigated these TSH cell adenomas with immunohistochemical and ultrastructural methods and compared their ultrastructural features with brefeldin A (BFA, 0.5 mg/ml) treated pituitary adenoma cells. BFA-treated pituitary adenomas include a prolactin (PRL) cell adenoma, a growth hormone (GH) cell adenoma, an adrenocorticotropic hormone (ACTH) cell adenoma, a gonadotroph adenoma, and a plurihormonal adenoma. Immunohistochemical staining disclosed that one of the TSH cell adenomas produced only TSH-beta and that another produces both TSH-beta and FSH-beta. Ultrastructural analysis showed the abundance of oval-shaped dilated rough endoplasmic reticulum (rER). Within the dilated rER, the mistlike deposit or deposit along the inner margin of the rER membrane was observed. On the other hand, BFA-treated cultured pituitary adenoma cells showed the opening of the cavity of the rER cisterna and they enlarged to an oval form with time and revealed an accumulation of electron-dense deposits within the dilated rER. These ultrastructural similarities between TSH cell adenoma and BFA-treated pituitary adenoma cells indicate the functional disturbances in the secretory passage through the Golgi apparatus in TSH cell adenoma cells.