Effect of hypo- and hyperthyroidism on binding of [3H]-nitrendipine to myocardial and brain membranes.

The density of calcium channel binding sites as determined by [3H]-nitrendipine binding was found to be decreased in hearts of hyperthyroid rats but hardly altered by hypothyroidism. In contrast, dihydropyridine binding sites in the cerebral cortex were unaffected by dysthyroid states. Myocardial [3H]-nitrendipine binding sites were also decreased after treatment of the animals with isoprenaline but not in spontaneously hypertensive rats. These findings suggest that myocardial hypertrophy is not necessarily accompanied by a loss of calcium channels and that thyroid hormone regulates the density of [3H]-nitrendipine binding sites in a tissue-specific manner.