A rapidly acting metabolite of vitamin D3.

A vitamin D(3) metabolite in intestine more polar than 25-hydroxy-vitamin D(3)(25-OH D(3)) has been detected by countercurrent distribution. The intestinal metabolite is found also after administration of labeled hydroxy D(3), indicating that it arises from vitamin D(3) via the intermediate 25-hydroxy derivative. The more polar metabolite is localized in the nuclear-chromatin fraction and appears in the gut before the physiological response to vitamin D(3).3.5 mug of the intestinal metabolite was isolated from 1250 chickens; the resulting purified material proved to be a potent mediator of calcium absorption. On a weight basis, it was at least 5 times as effective as vitamin D(3), and acted 3 times faster than either hydroxy D(3) or D(3) in stimulating intestinal calcium transport in the rachitic chick. It is proposed that this as yet uncharacterized steroid represents the active form of vitamin D(3) in the intestine.