Hormone production in pituitary adenomas following external irradiation

INTRODUCTION: The aim of this study was to investigate the hormone production in pituitary gland tumors following fractionated external irradiation in rats.

MATERIALS AND METHODS: Sixty female Wistar rats 3 to 4 month of age at the beginning of the experiments, were subjected to fractionated roentgen-rays exposure, 2 Grays (Gy) daily, either up to 20, 40 or 60 Gy. The animals were sacrificed either 6 month or 1 year after completion of the randomly assigned irradiation protocol.

RESULTS: We found 9 pituitary tumors in 60 irradiated rats (15%). All tumors proved to be adenomas. Immunohistochemical analysis of hormone production in remnants of the normal adenohypophysis revealed immunoreactivity for growth hormone (GH), adrenocorticotropic hormone (ACTH), prolactin (PRL), thyroid-stimulating hormone (TSH), and follicle-stimulating hormone (FSH). In adenomas, 4 cases were immunoreactive for TSH, 4 for GH, 2 for PRL, and 2 for FSH. The tumors were not reactive with anti-ACTH and anti-LH (luteinizing hormone).

DISCUSSION: We concluded that irradiation accelerates the development of pituitary gland adenomas. In our series these tumors were predominantly incidental findings at necropsies after pre-termed follow-up, with a variety of hormone producing tumor cells. However, 4 of 9 tumors in our study were not producing hormones.