Transfer of propionate by rat small intestine in vitro.

1. The transfer of propionate by sacs of rat everted intestine has been investigated in relation to a number of physico-chemical factors which affect movement of weak electrolytes.2. Neither the observed movement nor the distribution of propionate can be accounted for by the theory of non-ionic diffusion or by modifications of it, such as the microclimate hypothesis or partial permeability to ions.3. It is not possible to account for the observed propionate movement by the electrical potential across the gut or by solvent drag.4. The most satisfactory explanation for the observations is a transfer process in the gut for volatile fatty acids, and some features of this are discussed.