The effect of thyroid status on the calmodulin content of several tissues in the rat

The present studies represent an initial effort to evaluate a possible relationship between thyroid status and calmodulin and were undertaken because of evidence that some actions of the thyroid hormones are calmodulin mediated. To this end, the effects of hypothyroidism and of thyroid hormone excess on the concentration of calmodulin in several tissues of the rat were evaluated. In thymocytes, liver, heart, and brain, but not in skeletal muscle, calmodulin concentrations were markedly increased in the thyrotoxic rat (140-203% of values in normal controls); values were unchanged in hypothyroid animals. These changes were evident regardless of whether calmodulin concentrations were expressed per cell (thymocytes), or in relation to either the wet wt or protein content of the tissues. These findings are apparently the first to demonstrate that thyroid hormone, unlike other hormones tested thus far, can influence tissue calmodulin content. In view of the fact that many metabolic systems that are influenced by calmodulin are similarly affected by thyroid hormones, the findings support the possibility that some actions of thyroid hormone are calmodulin mediated.