Absorption of vitamin D3-3H in control subjects and patients with intestinal malabsorption.

Abstract

Tritium-labeled vitamin D3 of specific activity 5 to 15 [mu]c per mg was prepared by random exchange and isolated in crystalline form. Its properties were those of the authentic vitamin. Control subjects were given oral doses of 0.1 to 1 mg of vitamin D3-3H, containing 1.5 to 15 [mu]c of tritium, in arachis oil, and their plasma and fecal radioactivity was assayed during the subsequent 6 days. Radioactivity was present in the plasma 3 hours after a dose and at this stage was largely located in the chylomicrons. It reached a peak at 6-12 hr. and thereafter declined exponentially, with a mean half-life of 54 hr. The net absorption of 0.5- to 1-mg doses, calculated from the fecal excretion of radio-activity, ranged from 62.4 to 91.3%. The net absorption of 0.5- to 1-mg doses of vitamin D3-3H was also measured in patients with various forms of steatorrhea. Malabsorption of vitamin D3-3H was demonstrated in 5 patients with adult celiac disease, the degree of malabsorption being related to the fecal fat excretion. Malabsorption of vitamin D3-3H was also demonstrated in 3 patients with pancreatic steatorrhea and in 2 patients with biliary obstruction.