Factors affecting the absorption of vitamin B 12
Adams, J.F.; Clow, D.J.; Ross, S.K.; Boddy, K.; King, P.; Mahaffy, M.A.
Clinical Science 43(2): 233-250
1972
ISSN/ISBN: 0009-9287 PMID: 4625906 Document Number: 55915
The absorption of radioactive cobalamin was measured by whole-body counting in control subjects and in patients with pernicious anaemia. Absorption of cyanocobalamin by patients was decreased by charcoal but not by bile or saliva. Absorption of cyanocobalamin by controls was not affected by food but was significantly increased by pentagastrin. With pentagastrin absorption of cyanocobalamin was significantly greater than that of hydroxocabalamin. The pig intrinsic factor-mediated absorption of cyanocobalamin by patients was significantly depressed by pentagastrin. The effect of increasing the mass of pig intrinsic factor concentrate on the absorption of cyanocobalamin by patients could be described by a function relating the amount absorbed, the mass of intrinsic factor and two constants. The relation implies that when the mass of intrinsic factor is small the amount of cyanocobalamin absorbed is directly proportional to the mass of intrinsic factor but that absorption approaches a saturation value with increasing mass of intrinsic factor. In physiological terms the function implies that absorption is proportional to the amount of cyanocobalamin attached to receptor sites but that cyanocobalamin attached to receptor sites may become detached and either reattached or lost to absorption. With 25 and 50 mu g by mouth controls absorbed more cyanocobalamin and hydroxocobalamin than patients. With both amounts controls absorbed more cyanocobalamin than hydroxocobalamin but there was no difference in patients. The intrinsic factor mechanism therefore influences amounts absorbed from such doses and seems to be a factor in the differences in absorption of cyanocobalamin and hydroxocobalamin. The use of double-tracer techniques makes it possible for each subject to act as his own control in studies of vitamin B-12 absorption.