Effect of drugs on pituitary ultrastructure

Clinical Impact of the Current WHO Classification of Pituitary Adenomas

WHO classifications should be used for comparing the results from different groups of pathologist and clinicians by standardized histopathological methods. Our present report describes the important parameters of pituitary adenoma pathology as demand of the WHO classification for correlation to endocrine data and prognosis. The combination of HE stain based structures with immunostainings for pituitary hormones allows subclassification of adenomas as the best method not only for correlations to clinical hyperfunctions but also for statements to the sensitivity of drug therapies (somatostatin analogs, dopamine agonists). GH-, PRL- and ACTH-secreting pituitary adenomas are further classified based on the size and number of their secretory granules by electron microscopy, or as is mostly the case nowadays by cytokeratin staining pattern, into densely and sparsely granulated. Granulation pattern may be considered for the prediction of treatment response in patients with GH-secreting adenomas, since the sparsely granulated subtype was shown to be less responsive to somatostatin analog treatment. For prognosis, it is important to identify aggressive adenomas by measurements of the Ki-67 index, of the number of mitoses, and of nuclear expression of p53. Among the criteria for atypical adenomas, high Ki-67 labeling index and invasive character are the most important adverse prognostic factors. Promising molecular markers have been identified that might supplement the currently used proliferation parameters. For defining atypical adenomas in a future histopathological classification system, we propose to provide the proliferative potential and the invasive character separately.

[Effects of irradiation therapy and inhibiting drugs on the pituitary and its adenomas]

Radiation therapies of pituitary adenomas induce an increase in fibroses and nuclear pleomorphism. Most growth hormone (GH) secreting pituitary adenomas react to somatostatin analogues by a distinct decrease of GH secretion. In two thirds, levels of IGF-1 can be normalized. Some cases show a shrinkage of adenomas that correlates with fibrosis of the tumor. With these drugs, thyroid stimulating hormone secreting adenomas can also be treated. Prolactin secreting adenomas are mostly treated primarily with dopamine agonists. Up to 90% of cases show a strong decrease in hormone secretion and a distinct shrinkage of the adenomas based on strong decrease in adenoma cell volume. Long-term medication with high doses of glucocorticoids induces Crooke's cells in the anterior pituitary. These are suppressed ACTH cells and characterized by increased numbers of large lysosomes and dense bundles of cytofilaments.

Pituitary tumors: prognostic indicators

Many factors influence the proliferation of pituitary adenomas: angiogenesis, apoptosis, growth factors, oncogenes, tumor suppressor genes, and hormone receptors. These elements can be demonstrated by immunohistochemistry and/or molecular pathology but no single factor can be used for determination of biological behavior resp. prognosis. Pituitary adenomas can be enclosed or invasive and may be very large or may be microadenomas, but the most important point for prognosis is the total resection in the first or second surgery or the reaction on treatments by drugs. Especially for residual tumor tissue proliferation, markers are important because they may indicate the growth rate and the aggressiveness of the tumor. Radiation therapy is indicated in many of these recurrent tumors and can improve the prognosis.

[Dopaminergic and somatostatinergic pathways decrease serum thyrotropin in rats bearing the 256-Walker mammary carcinoma]

The hypothalamus-pituitary-thyroid axis was studied in rats with the "low T(3) syndrome" caused by the implantation of the Walker-256 mammary carcinoma. Male adult rats were injected s.c. with 1 x 106 viable tumoral cells and killed 10 days later. The tumor development was associated with decreased thyroid activity characterized by a approximately 15% reduction in the nuclear area of the thyrocytes and 131I-thyroid uptake (down by approximately 50%), as well as about 70% lower serum levels of T4 and rTg. The functional thyroidal response to exogenous TSH was decreased in the tumor-bearing rats, as well as the rTSH secretion in response to TRH (50 microg/kg). To investigate the role of other hypothalamic neuromediators in this process, tumor-bearing rats received an i.v. injection of metoclopramide (5 mg/kg) and/or physostigmine (12.5 microg/kg), with or without concomitant stimulus with TRH. Each drug improved the rTSH response to TRH, which in the case of physostigmine, almost normalized. When both drugs were injected simultaneously the rTSH response to TRH returned to normal. Thus, in addition to the well known alterations in the extrathyroidal metabolism of thyroid hormones, TSH secretion is decreased in rats with the Walker-256 tumor, indicating a generalized reduction in the thyroid function.

Pituitary physiological and ultrastructural changes during aging

Although it is known that both aged human beings and animals exhibit a decrease in pituitary hormone production and release, there is controversy about the true nature of these changes. Whereas some authors postulate an extra pituitary cause, i.e., a dopaminergic failure, others consider that the problem is at the level of the gland itself. CFW mice 2, 6, 12 and 18 months old, were i.p. inoculated withL: -Dopa. The pituitary gland was removed and sectioned, then observed and photographed in an electron microscope. Photomicrographs were scanned into a computer and digital image analysis made to determine secretory granules and organelle kinetics. Normal GH and TSH cells of elder mice responded to stimulation withL: -Dopa in a similar way as did cells of juveniles. The responsiveness rate of those cells to the amine precursor during the first hour of treatment was 38±3.5% and 26±0.3% of the studied cells in young and aged animals, respectively. Fully functional cells, i.e., GH and TSH cells showing 5 to 90% of their cytoplasm occupied by secretory granules (some of them immature), with a developed RER, and with absence of cell damage, were seen to be reduced from 98% in younger to 65.7% in aged animals. In successive steps, cells showed cell desquamation, darkened cytoplasm, differential swollen endoplasmic reticulum without secretory granules, increased number of secondary lysosomes (more than two per cell in a cross-section), differential swollen mitochondria, cytoplasm only containing two to five giant secondary lysosomes and finally, a complete loss of cell architecture. Therefore, GH and TSH cells at the end of their life-span were seen to derive into apoptotic images. In the whole gland, an increasing number of those pathologic images were seen as aging proceeded, thus reducing the number of normal and productive cells. From the results presented here it is proposed that an extrapituitary failure is insufficient to explain the reduced production of GH and TSH, and that the problem evolves also at the level of the gland itself.