Absorption of inorganic ions and volatile fatty acids in the rabbit caecum

1. Rabbit caecal segments in situ were used to measure absorption rates of volatile fatty acids (VFA) and inorganic ions from a saline solution comparable in composition to normal caecal fluid. 2. Results confirm the importance of VFA absorption from caecal material found by other workers. 3. Like the mammalian colon, the rabbit caecum conserved large amounts of sodium, chloride and water. Bicarbonate was also absorbed. 4. VFA replacement studies showed that net water absorption was reduced, net electrolyte absorption was hardly influenced. 5. Na replacement completely inhibited net water absorption and decreased net VFA and Cl absorption, HCO3 was heavily secreted. 6. These findings indicate that VFA absorption in the rabbit caecum is partly dependent on Na absorption and that in the absence of Na an anion-exchange mechanism occurs.