Effect of 1,25-dihydroxyvitamin D3 on calcium absorption in the colon of healthy humans

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Abstract
Ca absorption in patients with short bowel syndrome is significantly higher when the colon is left intact. Whether exogenous 1,25-dihydroxyvitamin D3 [1,25(OH2)D3] can induce or enhance colonic Ca absorption in healthy subjects ingesting a normal diet was investigated. Steady-state colon perfusion studies were performed before and after 1 wk of 1,25(OH)2D3 administration (2 .mu.g/day, 10 subjects). Serum 1,25-dihydroxyvitamin D concentration rose from 23.0 .+-. 2.2 to 39.5 .+-. 4.3 pg/ml (mean .+-. SE, P < 0.01). In the basal state the mean net movement of Ca was not significantly different from 0 when a 5 mM calcium gluconate solution was perfused (100 .+-. 84 .mu.mol .cntdot. h-1 .cntdot. entire colon secreted-1). Vitamin D adminstration resulted in a significant change toward Ca absorption (106 .+-. 47 .mu.mol .cntdot. h-1 .cntdot. entire colon absorbed-1, P < 0.02). 1,25(OH)2D3 had no effect on colonic Mg phosphate, water, and electrolyte movement. In healthy humans exogenous 1,25(OH)2D3 apparently can change colonic Ca movement toward absorption. Similar changes in colonic Ca transport could be caused by endogenous 1,25(OH)2D3 when Ca deficiency has occurred in short bowel syndrome.