The effects of variations in vitamin D and calcium intake on parathyroid weight and amino acid uptake were studied in vivo. D-deficient rats on low or normal calcium intake developed hypocalcemia, parathyroid enlargement, and increased parathyroid uptake of α-aminoisobutyric acid (AIB). D-deficient rats fed a high-calcium diet and D-treated rats fed a normal-calcium diet had normal serum calcium concentrations, smaller parathyroids, and lower parathyroid uptake of AIB. When serum calcium concentration of vitamin D-deficient rats was increased acutely by vitamin D treatment, dietary lactose, or injection of calcium, parathyroid uptake of AIB decreased. Low-calcium medium stimulated and high-calcium medium suppressed AIB uptake of parathyroids from vitamin D-deficient rats in vitro. Parathyroids from vitamin D-deficient rats secreted bone-resorbing material in tissue cultures. The data indicate that both size and functional activity of rat parathyroids are inversely related to serum calcium concentration, and do not depend on the presence or absence of vitamin D.
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Au et al. (1965) studied this question.