The tissue localization of tritiated parathyroid hormone in thyroparathyroidectomized rats.

Tritiated acetamidino-parathyroid hormone localizes rapidly and specifically in the kidneys of thyroparathyroidectomized rats within 30 min after subcutaneous injection. There is some indication of saturation of the kidney by the hormone very early after injection with doses of greater than 40 pg per rat. The hormone is metabolized rapidly to trichloroacetic acid-soluble components with a resultant rapid loss of radioactivity from the kidney. Localization in bone is not demonstrable when data are calculated on a tissue weight basis. When calculated as disintegrations per min per g of cells, the bone cells are more radioactive than any other. However, direct evidence for binding to bone cells is not available. It was established that the radioactivity in bone is not due to vascular parathyroid hormone. Localization of 3H-labeled parathyroid hormone in kidney is less when the parathyroid glands are not removed, suggesting competition by endogenous parathyroid hormone. Neither [3H]insulin or methyl [3H]acetimidate localize in the kidney in the same manner as does parathyroid hormone, but oxidized, inactive, parathyroid hormone binds to kidney in a manner identical with native hormone.