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Permeability to Thiamin of the Sheep Rumen Wall in Vitro¹

Institute of Physiology, School of Veterinary Medicine, Hannover, Federal Republic of Germany

Abstract

In vitro experiments were conducted to study the permeability to thiamin of sheep rumen wall in either direction. Isolated discs of rumen wall mucosa were used in incubation experiments over 3 hr, controlled by measurements of transmural potentials. In some experiments ¹⁴C-labeled thiamin was used.

At thiamin concentrations in the mucosal fluid ranging from .1 to 1.6 µg/ml no changes of the initial concentrations were found after incubation, whereas, at higher concentrations (3.2 to 12.8 µg/ml) there was a slight but insignificant decrease. In no case did the initial serosal thiamin concentration change. When 2.0 µg/ml ¹⁴C-thiamin were applied a minor reduction of ¹⁴C-activity in the mucosal fluid was found.

When .05 to .2 µg/ml thiamin were applied in the serosal bathing fluid no concentration changes measurable by chemical analysis were obtained. Experiments with ¹⁴C-thiamin showed that approximately the same amount of ¹⁴C-thiamin migrated into the rumen mucosa as in the opposite direction.

No accumulation of ¹⁴C-thiamin in the rumen mucosa occurred during incubation.

The results indicate that the rumen wall mucosa of sheep has an extremely low permeability to thiamin and that the rumen may not be considered as a site of significant absorption or endogenous secretion of thiamin.

¹ This investigation was supported by a grant of the German Research Scoiety (Deutsche Forschungsgemeinschaft DFG).

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