SALMON-CALCITONIN INDUCES PITUITARY-TUMOR IN RATS

Calcitonin is widely used in the treatment of post-menopausal osteopor osis. The present study was designed to investigate the effects of sal mon calcitonin (SCT) on the incidence of the pituitary tumors in Sprag ue-Dawley (SD) rats. Subcutaneous injections of SCT at a dose of 160 I U/kg/day for 6 months reduced body weight and induced one pituitary hy perplasia and three pituitary adenomas in 4 of 5 animals, while 5 cont rols did not show any changes. Prolactin-positive cells were located a t the periphery of the affected pituitaries adjacent to the prolactin- negative adenomas. In addition, serum concentrations of prolactin and TSH were lower than in the controls, although serum calcium or LH leve ls were not significantly different from the controls. Among 7 animals treated with SCT for 6 months followed by no medication for another 6 months, 5 adenomas were detected, one of which had invasive growth to ward the adjacent tissue, whereas only one adenoma was found in 9 cont rols. These results suggest that SCT administration at a high dose may induce the formation of pituitary adenoma, or may accelerate the deve lopment of spontaneous pituitary adenomas, some of which show frequent mitotic figures and invasive growth into the surrounding tissue, poss ibly resulting in malignant transformation. This indicates the need fo r caution in considering whether calcitonin injections into patients w ith osteoporosis as well as Paget's disease may induce such pituitary tumors.