Countercurrent Multiplication of Sodium in Intestinal Villi during Absorption of Sodium Chloride

The sodium and the potassium concentrations in the villous tissue, expressed as g Na or K per nig tissue protein, were determined in vivo along the villous length during the absorption of isotonic saline solutions. The sodium concentrations was found to be 3 4 times higher at the tip than at the villous base. The addition of 30 mmol glucose to the incubation medium resulted in a significant increase of the sodium concentration along villous length, while this gradient was drastically decreased by ischemia or intense vasodilatation as well as by intraarterial infusion of ouabain. The intracellular sodium and potassium concentrations at the villous base were calculated to 21 and 125 mEq/1, respectively, during isotonic saline absorption. The extracellular sodium concentration at the villous tip was estimated to 300–900 mEq/1, corresponding to an interstitial osmolarity of 600–1600 mOsm/1. It is proposed that a counter‐current multiplication of sodium occurs in the villi resulting in a high interstitial osmolarity at the villous tip. The functional importance of the countercurrent multiplication of sodium for the absorption of water is discussed.