Physiological concentrations of 24,25-dihydroxyvitamin D3 rapidly decrease the in vitro intestinal calcium uptake in the Atlantic cod, Gadus morhua.

The effects of physiological concentrations of 1,25(OH)2D3 and 24,25(OH)2D3 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 45Ca. At 2.02, 4.04, 10.1, and 20.2 nM 24,25(OH)2D3 decreased the Ca2+ influx across the intestinal mucosa by 21, 31, 34, and 28%, respectively, whereas perfusion with 1,25(OH)2D3 (concentrations: 85.3, 128, 256, and 640 pM) had no effect. The actions of 24,25(OH)2D3 were dose-related, observed within 10 to 25 min, and are concluded to affect intestinal Ca2+ influx via a rapid nongenomic mechanisms; 1,25(OH)2D3 seems to be without transcaltachic effect. Thus, for the rapid, short-term regulation of intestinal calcium uptake in the Atlantic cod, 24,25(OH)2D3 is a more important vitamin D3 metabolite, in contrast to other vertebrates in which 1,25(OH)2D3 is of major importance.