Role of kidney tissue in the production of 25-hydroxyvitamin D3-26,23-lactone and 1 alpha, 25-dihydroxyvitamin D3-26,23-lactone.

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Abstract
Labeled 25-hydroxyvitamin D3-26,23-lactone was isolated from the serum of vitamin D-repleted rats given [3.alpha.-3H]-25-hydroxyvitamin D3 24 h prior to sacrifice. The metabolite was identified by cochromatography with the authentic lactone on straight-phase and reversed-phase high-performance liquid chromatograhy. Production of the lactone was abolished by nephrectomy indicating that the kidney is the site of synthesis. Homogenate of kidneys from chickens given large doses of vitamin D can carry out in vitro production of the lactone from 25-hydroxyvitamin D3. When 1.alpha.,25-dihydroxyvitamin D3-26,23-lactone. Incubation of rachitic chicken kidney homogenates with 25-hydroxyvitamin D3-26,23-lactone produced substantial amounts of a compound that was identified by mass spectrometry as 1.alpha.,25-dihydroxyvitamin D3-26,23-lactone. The development of a functional group on C-26 and eventual lactone formation takes place in kidney by a system acting on 25-hydroxyvitamin D3.