Effect of altered thyroid status on lysosomal enzymes and thymidylate synthetase activity in tumors and livers of host animals.

The purpose of this study was to determine whether or not alternations in tumor growth induced by changes in thyroid status were mediated through changes in key enzymes, whose activity is known to be influenced by thyroid hormones. The activities of three lysosomal enzymes (cathepsin B1, cathepsin D, and acid phosphatase) and thymidylate synthetase were measured in implanted mammary tumors as well as in the livers of host animals that were either euthyroid, hypothyroid, or hyperthyroid. Hypothyroidism produced no significant change in enzyme activity in the tumors. Hyperthyroidism, on the other hand, did cause a significant increase in the activity of all lysosomal enzymes in the tumors, but did not affect thymidylate synthetase levels. In the livers of the host animals, hypothyroidism produced a significant decrease in cathepsin B1 and a significant increase in acid phosphatase but did not change cathepsin D or thymidylate synthetase levels. Hyperthyroidism produced a significant increase in all enzymes measured in the livers of the host animals. The significant decrease in tumor weight with hypothyroidism did not correlate with the insignificant changes in the enzymes tested. Similarly, there was no correlation between the significant increase in the enzymes levels found with hyperthyroidism and the insignificant change in tumor weight.