Independence of Transfer of Solute and Solvent across the Rat lleum

Abstract

FROM experiments on the rat ileum in vitro Fisher¹ and Smyth and Taylor², using glucose-free media and metabolic inhibitors, suggested that the movement of water across the ileum was an active, metabolic dependent process. Parsons and Wingate³ observed that net movement of water took place agains⁴ an osmotic gradient, that is, with the mucosal solution hypertonic to tha serosal there was a net water movement from tne mucosal to the serosal surface. These workers again suggested that the process was an active one relatively independent of osmotic forces. Also, Smyth and Taylor⁴ using a glucose-free medium with isolated rat ileum found that the water movement was lowered in the absence of glucose and interpreted the process of water movement as being an active one. Hendley and Smyth⁵ have reported experiments showing that the concentration of sodium in the fluid appearing on the serosal surface is higher than the concentration on the mucosal surface of the rat intestine, indicating that there was active sodium transport, but have drawn no conclusions as to its primary role in solvent movement. Curran and Solomon⁶ and Curran⁷, on the other hand, have shown, both in vivo and in vitro, that the movement of water across the rat ileum is secondarily dependent on active transport of solute. Removal of the glucose from the medium results in a lowering of the solute transport and hence a fall in water movement. Similarly, using metabolic inhibitors the primary action of these was demonstrated to be on the salt transport mechanism and the water movement was shown to be only a secondary effect. Furthermore, the experiments of Curran⁷ show that, with isotonic conditions on both sides of the gut, a gradient of water activity is established as a result of the net solute transfer, and this is sufficient to explain the net solvent movement, thus affirming the passive nature of the water transfer.