The influence of hyper- and hypothyroidism on the incidence of lymphatic leukemia of AKR mice.

While much is known about the influence of the estrogens, androgens, and adrenocortical hor mones on experimental leukemia, very little has been published on the effect of the thyroid gland on this disease. However, it has been assumed that the thyroid might play a role in leukemia, inas much as lymphocytosis is frequently observed in hyperthyroid subjects; moreover, growth of lym phatic tissue occurs in thyroxine-treated animals, while thyroidectomy has the reverse effect (12, 13, 17). Several authors have also described elevated metabolic rates in leukemia (9, 11, 15, 21), some even claiming that the basal metabolic rate was a truer indicator of the severity of the process than the leukocyte count (9, 11, 15, 19). Furthermore, the blood iodine was described as being elevated in a considerable number of patients with lymphoid leukemia (21). Finally, thyroidectomy has been claimed to produce a striking remission in a case of chronic lymphatic leukemia (5). While the reports thus far described have tended to suggest that the thyroid is hyperactive in lym phatic leukemia, the following findings contradict this: the serum cholesterol level of patients with lymphatic leukemia was normal on the average (21), as was also the thyroidal I131 uptake in fourteen of fifteen leukemic patients, ten of whom had increases in the basal metabolic rate (1). This suggests the nonparticipation of the thyroid gland in the elevation of the basal metabolic rate of leukemic patients, and some authors have sug gested protein catabolism as the major factor in the increased gaseous metabolism (2). Further more, chronic thyroid administration did not significantly alter the incidence of radiationinduced tumors in C57BL mice (14), and thiouracil similarly failed to influence lymphoma growth in R3 mice (22) or in humans (3). Methylthiouracil was also ineffective in two cases of myelogenous leukemia (10). However, a preliminary experiment in our laboratory revealed that thyroxine de creased, while thiouracil increased the incidence