Radiochromium distribution in thyroid and parathyroid deficiency

Body retention and tissue distribution of a 51chromium (Cr) tracer were studied in thyroparathyroidectomized (TPTX) rats and in TPTX rats after replacement with thyroxin, calcitonin, or parathyroid hormone. A tracer dose containing 1 ng Cr or less and 0.5 to 0.7 muCi of high specific activity 51Cr (Cr III) was injected intravenously in control, TPTX, and TPTX animals receiving hormone replacement. Three days later, the 51Cr content of the serum and various tissues was determined and the data were expressed as percent dose per milliliter or gram and as tissue: serum 51Cr ratios. TPTX resulted in a significant increase in total body 51Cr retention and 40 to 240% increases in serum and tissue 51Cr levels. Tissue:serum 51Cr ratios were uniformly depressed. Replacement with thyroxin completely or partially reversed these changes in all tissues studied except bone. Calcitonin and parathyroid hormone had no consistent effect on body, serum, or tissue 51Cr levels. These data, indicating that 51Cr distribution is influenced by thyroid hormone activity but not by calcitonin or parathyroid hormone, are compatible with the hypothesis that thyroid hormone controls cellular Cr transport.