25-Hydroxycholecalciferol Metabolism in Hypophysectomized Rats*

The metabolism of 25-hydroxycholecalciferol (25-(OH)Da) was investigated in vitamin D normal rats, 4 weeks after hypophysectomy. Compared to sham-operated controls, these animals were hypophosphatemic and their parathyroid glands were significantly smaller than normal. Eighteen hours after ip injection of a single dose of tritiated 25-(OH)D3 (50 pmol), chromatography of serum extracts on Sephadex LH-20 and high pressure liquid chromatography showed that the percentage of radioactivity corresponding to 24,25-dihydroxycholecalciferol [24,25-(OH)2D3] was significantly higher in hypophysectomized rats (11.7 ± 0.95% vs. 6.9 ± 0.78%). No radioactivity was detected in the area corresponding to 1,25-dihydroxycholecalciferol. In hypophysectomized rats injected 2 weeks with radioactive 25-(OH)D3 the amount of 24,25(OH)2D3) was still higher than in sham-operated controls. Parathyroidectomy 48 h before the injection of [2H]25(OH)D3 abolished the difference between the two groups. The percentage of 24,25-(OH2D3t in th...