| Abstrakt: |
Our data show that injections of thyroxin do not increase the rate of intestinal absorption of thiamin chloride in rats as they do in the case of dextrose and other substances susceptible to phosphorylation. This observation would indicate that phosphorylation plays no dominant part in determining the rate of intestinal absorption of thiamin or that thyroxin has no stimulating effect on the rate of enzymic formation of the pyrophosphate ester linkage. The stimulating effect of thyroxin may be limited to the phosphorylating processes involving the mono-phosphoric acid ester, as in the transport of dextrose across the intestinal mucosa. The conclusion that phosphorylation plays no part in the intestinal absorption of thiamin is supported also by the work of Ochoa,10who found that in vitrointestinal tissue, in contrast to liver tissue, possesses little ability to phosphorylate thiamin.Two observations made during the course of our experiments indicate that absorption of thiamin in the intestine probably takes place by means of simple diffusion. First, the rapid initial absorption of thiamin is succeeded by a much slower rate of absorption, presumably after the diffusion equilibrium between the lumen of the gut and the intestinal mucosa has become established. Secondly, absorption of thiamin is roughly proportional to its concentration in the intestine, as was seen when the dose of thiamin was increased from 100 μg to 1 mg. On the other hand, if the absorption of a substance is aided by phosphorylation, as, for instance, is the case with dextrose, the rate of absorption remains constant and is within wide limits independent of the concentration of the substance which is being absorbed. |
