PHYSIOLOGICAL CONCENTRATIONS OF 24,25-DIHYDROXYVITAMIN D-3 RAPIDLY DECREASE THE IN-VITRO INTESTINAL CALCIUM-UPTAKE IN THE ATLANTIC COD, GADUS-MORHUA

The effects of physiological concentrations of 1,25(OH)(2)D-3 and 24,25(OH)(2)D-3 on the intestinal Ca2+ uptake in the Atlantic cod (Gadus morhua) were investigated. The intestine was perfused, in vitro, both vascularly and through the intestinal lumen, and the Ca2+ influx was measured using Ca-45. At 2.02, 4.04, 10.1, and 20.2 nM 24,25(OH)(2)D-3 decreased the Ca2+ influx across the intestinal mucosa by 21, 31, 34, and 28%, respectively, whereas perfusion with 1,25(OH)(2)D-3 (concentrations: 85.3, 128, 256, and 640 pM) had no effect. The actions of 24,25(OH)(2)D-3 were dose-related, observed within 10 to 25 min, and are concluded to affect intestinal Ca2+ influx via a rapid nongenomic mechanism; 1,25(OH)(2)D-3 seems to be without transcaltachic effect. Thus, for the rapid, short-term regulation of intestinal calcium uptake in the Atlantic cod, 24,25(OH)(2)D-3 is a more important vitamin D-3 metabolite, in contrast to other vertebrates in which I,25(OH)(2)D-3 is of major importance. (C) 1995 Academic Press, Inc.