Abstract
Summary
The 6-hour distribution of a tracer dose of Ca45 was studied in rats at various intervals after parathyroidectomy and sham operation. In young rats studied one day after parathyroidectomy there was a marked decrease in plasma calcium and a small decrease in the “6-hour exchangeable calcium.” One week after parathyroidectomy there was no further decrease in plasma calcium but a significant further decrease in 6-hour exchangeable calcium. In old rats studied one week after parathyroidectomy there was a somewhat smaller decrease in plasma calcium concentration and no change in 6-hour exchangeable calcium. It is concluded that removal of the parathyroids does not affect the amount of bone calcium available for exchange directly, but may act indirectly in the following sequence: decreased parathyroid hormone → decreased bone resorption → decreased new bone formation → decreased exchangeable calcium.
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