Immunohistochemical studies of early changes of pituitary glands induced by synthetic salmon calcitonin (sCT) in Sprague-Dawley rats - Experimental models for the human alpha-subunit-producing pituitary adenomas

To elucidate the effects of synthetic salmon calcitonin (sCT) on the cells in the rat pituitary gland, we histopathologically and immunohistochemicall y examined the early changes, after 4 or 13 weeks treatment with sCT 120 IU /kg. Focal proliferative lesions of the anterior pituitary glands were foun d in 100% of the cells after treatment for 13 weeks with sCT. Histologicall y, the cells which make up the focal proliferative lesions were classified into the following groups, i.e., 1) enlarged basophilic focus, 2) vacuolate d cell focus and 3) chromophobe cell focus. The majority of nuclei in those focal proliferative lesions were positively stained by BrdU. Furthermore, those focal proliferative lesions had positive staining for only the alpha- subunit and failed to show Pit-1 protein. Thus, sCT-induced pituitary tumor s are considered to be endocrinologically inactive, pure alpha-subunit-prod ucing tumors. Therefore, these tumors were thought to be potentially useful models of pure alpha-subunit-producing pituitary tumors in humans.