REGULATORY HYPERPARATHYROIDISM IN A PIG BREED WITH VITAMIN D DEPENDENCY RICKETS

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Abstract
A radioimmunoassay for porcine parathyroid hormone was developed and applied to measure immunoreactive parathyroid hormone (PTH) in plasma of pigs with hereditary vitamin D dependency rickets (VDDR) (pseudovitamin D deficiency rickets). Levels of 25-hydroxycholecalciferol (25-(OH)-D3) in plasma were measured by a protein binding assay. Both plasma concentrations of PTH and 25-(OH)-D3 showed an approximately 4-fold increase compared to normal pigs. PTH levels increased with duration of the disease. Daily dosing of the animals with 1-4 .mu.g of 1,25-dihydroxycholecalciferol (1,25-(OH)2-D3) reduced PTH concentrations and resulted in clinical healing. I.v. administration of 10 .mu.g of 25-(OH)-D3 per day did not alter PTH concentrations nor the clinical symptoms. These animals apparently suffer from regulatory hyperparathyroidism. The metabolic defect could be due to a failure of the kidney to convert 25-(OH)-D3 to 1,25-(OH)2-D3.

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