Two sites of bile formation as determined by mannitol and erythritol clearance in the guinea pig.

If water and inert solutes are assumed to pass from blood to bile through a fixed population of membrane pores, the changes in clearance produced by dehydrocholate suggest that osmotic filtration rather than diffusion is the predominant mode of transfer for mannitol and erythritol. Bile produced in the canaliculi is modified in the interlobular ducts by the action of secretin. If distal fluid transfer is an important determinant of the choleresis evoked by dehydrocholate, the mechanism appears to effect a net secretion or reabsorption of fluid at a rate roughly proportional to the rate of flow in the canaliculi.