BONE MINERALIZATION AND METABOLISM OF 25-HYDROXYVITAMIN-D3-H-3 IN THYROPARATHYROIDECTOMIZED RATS TREATED WITH PARATHYROID EXTRACT

Thyroparathyroidectomized rats fed a diet containing 1.2% calcium, 0.55% phosphorus maintain normal serum levels of these ions. Treatment of such rats with parathyroid extract (PTE; 20 U/100 g twice daily; 10 days) has no statistically significant effect on rates of bone formation, matrix apposition, or osteoid maturation. Significant decreases in osteoid width and mineralizing front width, as well as a 60% increase in the rate of initial mineralization were observed in the PTE-treated group. Conversion of3H-25-hydroxyvitamin D3 to3H-1,25-dihydroxyvitamin D3 was 4-fold higher in the PTE-treated group than in the untreated animals. Increased formation of 1,25-dihydroxyvitamin D3 in response to treatment with PTE may play a major role in correcting the mineralizing defect resulting from thyroparathyroidectomy. © 1979 Springer-Verlag.