Vitamin K2 absorption by rat everted small intestinal sacs

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Abstract
Small intestinal absorption of vitamin K2 was investigated in vitro. Experiments with increasing vitamin concentrations up to 900 nM revealed linearity between the concentration and the rate of absorption (r = 0.99). Addition of metabolic uncouplers and inhibitors such as 2,4-dinitrophenol, sodium azide and KCN did not decrease the rate of absorption of the vitamin (P > 0.05). Absorption rate of the vitamin increased when taurocholate was replaced by a nonionic detergent, Pluronic F-68. The addition of butyric and octanoic acids to the incubation solution caused an increase in the absorption rate of vitamin K2. No change in the adsorption of the vitamin occurred in the presence of oleic and linoleic acids. Addition of vitamins K1 and K3 to the incubation solution did not change the rate of vitamin K2 absorption. Vitamin K2 may be absorbed by the small bowel by a passive noncarrier-mediated diffusion process. The rate of diffusion varied when the lipid and bile salt composition of the incubation solution was modified. Distal intestinal absorption of vitamin K from bacterial sources coupled with colonic absorption of the vitamin may be the major constant source of vitamin K in mammals.