Villous tissue osmolality, water and electrolyte transport in the cat small intestine at varying luminal osmolalities.

Villous tissue osmolality and net transport for water, sodium, potassium and chloride were determined in the feline small intestine when exposing the mucosa to solutions with different mannitol concentrations (0, 100, 315 and 600 mmol/l). Tissue osmolality at the villous tip varied with luminal osmolality. At the villous base, on the other hand, tissue osmolality remained around the plasma osmolality regardless of the osmolality of the luminal fluid. Transport rates for water were affected in the way predicted from the lumen to tissue osmolality difference. A net flux from tissue to lumen was always recorded for the studied electrolytes. The hydraulic conductivity (Lp) of the intestinal epithelium with dilated intercellular spaces was estimated from the present results to be around 30 x 10(-12) cm x s-1 x Pa-1. When the intercellular spaces were collapsed Lp was estimated to be 15 x 10(-12 cm x s-1 x Pa-1.