Metabolism of Vitamin D. I. Preparation of Radioactive Vitamin D and Its Intestinal Absorption in the Rat*

Abstract

Methods are described for the chemical preparation of H3-vitamin D3 and of uniformly labeled C14-vitamin D2 from C14-ergosterol synthesized by yeast. The intestinal absorption of the labeled compounds was studied in vivo in the rat.Vitamin D is absorbed maximally in the jejunum and transferred chiefly into lymph.It was found mainly in the chylomicron fraction, as the free, biologically active sterol.Bile salt, specifically taurocholate as compared to taurodeoxycholate and taurochenodeoxycholate, is required for optimal absorption. 2 Steps can be distinguished in the transport across the intestine: uptake at the mucosal surface, relatively rapid, and transfer to lymph, relatively slow.Absorption is more rapid from mid-jejunal as compared to distal ileal segments primarily because the first, mucosal uptake step is more rapid and complete.