Role of the hypophysis in the regulation of vitamin D metabolism.

Hypophysectomy of animals given maintenance levels of vitamin D and adequate levels of dietary calcium and phosphorus brings about a marked reduction in plasma 1,25-dihydroxyvitamin D3 levels and a significant elevation in plasma 24,25-dihydroxyvitamin D3 levels. The hypophysectomy, as expected, results in reduced growth and lowered plasma levels of inorganic phosphorus. The injection of growth hormone markedly increases plasma levels of 1,25-dihydroxyvitamin D3 in hypophysectomized animals while bringing about a reduction in 24,25-dihydroxyvitamin D3 levels. These results support the idea that the hypophysis plays a role in the regulation of vitamin D metabolism and that growth hormone either directly or indirectly is one of the hypophyseal factors bringing about this regulation.