Studies of Tsh-producing Cells in the Pituitary and Expression of Growth Factors in Thyroidal Prolif- Erative Lesions in Rats Treated with Thiourea and Excess Vitamin

Changes of TSH-producing cells in the pituitary and thyroid expression of the growth factors , transforming growth factor a(TGFcr) and epidermal growth factor receptor (EGFR), as well as cyclin Dl, were inyestigated immunohistochemically in order to clarify their contribution to the enhancing effects of excess yitamin A (VA) on thyroidal carcinogenesis induced by thiourea (TU). Male rats were alloFated to 4 groups, control, TU, VA, and TU+VA, respectively, receiving no treatment, water contmnmg O,2% TU, diet centaining O.1% VA, and both for IO or l9 weeks afler a single s.c. injection of DHPN (2800 mglkg) for inltiation, Immunohistochemistry using antibodies against TSH demonstrated enlargement of TSH-producing cells in the TU+VA group as cempared to the TU group, supporting our concluslon that enhanced TSH stimulation is mainly responsible for promoting the effects of excess VA. Since the expression of TGFa , EGFR, and cyclin Dl in thyroid proliferatiye lesions did net exhibit any dififerences between the TU and TU+VA groups in the present study, these factors are unlikely to participate in VA enhancement Qf carcinogenesis.