Prevention of parathyroid hormone-dependent nephrocalcinosis by chronic administration of the organic phosphorothioate WR-2721

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Abstract
Pharmacological inhibition of parathyroid hormone (PTH) secretion has been the object of several experimental and clinical trials in the past. It is only recently that a drug, WR-2721 [S-,2-(3-aminopropylamino)-,ethylphosphorothioic acid], has been shown to effectively inhibit PTH secretion in euparathyroid subjects and in parathyroid cancer patients within a few hours after its administration. In the present study we tested its long term efficacy as a PTH inhibitor in a model of nephrocalcinosis resulting from secondary hyperparathyroidism. Intact and thyroparathyroidectomized (TPTX) rats were pair-fed on a low Ca (0.2%)-high phosphorus (1.6%) diet (nephrocalcinotic diet) or on a normal Ca (1.1%)-normal phosphorus (0.8%) diet for 7 days. Simultaneously, either 0.2 mmol/kg of WR-2721 or its solvent was injected subcutaneously twice daily. The intact animals on the nephrocalcinotic diet had an increased urinary cyclic AMP excretion and important renal Ca accumulation. This nephrocalcinosis was markedly reduced by WR-2721 treatment. The kidney Ca content of the WR-2721-treated rats was 58±6% lower than that of the nontreated animals. The low Ca-high phosphorus diet did not cause nephrocalcinosis in the TPTX rats. WR-2721 failed to reduce the nephrocalcinosis induced by 1,25 dihydroxyvitamin D3 intoxication in TPTX rats fed the normal Ca-normal phosphorus diet. In conclusion, the present study suggests that chronic treatment with WR-2721, a potent inhibitor of PTH secretion, may be effective for preventing the deleterious consequences of hyperparathyroidism, such as nephrocalcinosis.