Permeability to thiamin of the sheep rumen wall in vitro.

In vitro experiments were conducted to study the permeabil i ty 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 14 C-labeled thiamin was used. At thiamin concentrations in the mucosal fluid ranging from .1 to 1.6/ag/ml no changes of the initial concentrations were found after incubation, whereas, at higher concentrations (3.2 to 12.8 /~g/ml) there was a slight but insignificant decrease. In no case did the initial serosal thiamin concentration change. When 2.0 /lg/ml 14 C-thiamin were applied a minor reduction of 14C-activity in the mucosal fluid was found. When .05 to .2/~g/ml thiamin were applied in the serosal bathing fluid no concentrat ion changes measurable by chemical analysis were o b t a i n e d . Experiments with taC_thiamin showed that approximately the same amount of l acth iamin 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 permeabili ty to thiamin and that the rumen may not be considered as a site of significant absorption or endogenous secretion of thiamin. (