Elevated levels of colloid osmotic pressure in cecal contents of germfree animals.

Determinations of colloid osmotic pressure in the supernatant of germfree rat cecal contents indicated substantially elevated values in comparison to those of rat blood plasma or of conventional rat cecal supernatant. The germfree cecal supernatant, under conditions of similar total osmolality, was able to draw water at a sizable rate from a polyvinylpyrollidone solution whose colloid osmotic pressure was taken to be equivalent to that of interstitial fluid. It is suggested that the water absorption inhibition which was observed in the lower bowel of germfree rodents, is in part caused by the colloid osmotic pressure gradient which exists in these animals between the luminal contents and the tissue component.