title: The mechanism of the action of growth hormone on vitamin D metabolism in the rat.
abstract: GH has been shown to stimulate intestinal calcium absorption in rats and humans. We have investigated in rats whether GH might affect intestinal calcium absorption by stimulating the production of 1,25-dihydroxyvitamin D3 [1,25-(OH2D3], the active metabolite of vitamin D3. The tissue distribution of [3H]1,25-(OH2D3 8-40 h after iv injection of [3H]25-hydroxyvitamin D3 ([3H]25OHD3) was measured in sham controls, hypophysectomized, and GH-treated hypophysectomized rats. Since the plasma disappearance rate of iv [3H]1,25-(OH)2D3 was not significantly affected by hypophysectomy, the recovery of [3H]1,25-(OH)2D3 after [3H]25OHD3 administration was taken to be an indirect measure of renal 25-OHD3-1-hydroxylase. Hypophysectomy was found to reduce the recovery of [3H]1,25-(OH)2D3 from serum and intestinal mucosa by 70 +/- 2% (range). A 6-day course of GH treatment of hypophysectomized rats restored the formation of 1,25-(OH)2D3 to normal, and a significant effect was noted within 2 days, before any increase in renal weight was detectable. No other pituitary hormones appeared to be necessary. The markedly atrophic intestinal mucosa of hypophysectomized rats incorporated iv [3H]1,25-(OH)2D3 normally. However, it remains to be determined whether 1,25-(OH)2D3 alone can correct the decreased calcium transport in hypophysectomized rats.
mesh_terms: D000818:Animals; D001711:Biotransformation; D004100:Dihydroxycholecalciferols / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology*; D007016:Hypophysectomy; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D013997:Time Factors; D014807:Vitamin D / Q000378:metabolism*
chemical_list: D004100:Dihydroxycholecalciferols; D014807:Vitamin D; D013006:Growth Hormone