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Intestinal Absorption of Sodium and Potassium in the Laying Fowl¹

Department of Animal Science, The Volcani Institute of Agricultural Research, and The Weizmann Institute of Science, Rehovot, Israel

The relationships between the Na⁺ and K⁺ concentrations in the intestinal contents and their net absorption were studied in laying hens fed diets containing either 0.15 or 0.07% sodium (high Na and low Na, respectively). Yttrium-91 served as a reference substance for measuring the intestinal cation absorption in vivo. In the contents of the various intestinal segments, 46 to 87% of the Na⁺ and 47 to 97% of the K⁺ were ultrafilterable. A large net secretion of cations, especially Na⁺, occurred in the upper gastrointestinal tract, regardless of diet. Na⁺ absorption occurred along the entire small intestine, whereas K⁺ was absorbed in the jejunum but secreted in the ileum. In the ileum, Na⁺ absorption and K⁺ secretion were greater in the low as compared to the high sodium birds. This resulted in a reciprocal relationship between the concentrations of the two cations in this segment. The relationship between the diffusional driving forces and net cation absorption at the absorption sites indicated that Na⁺ was always absorbed against, and K⁺ along its respective gradient. K⁺ was secreted against its gradient into the ileum. The implications of these results with regard to the in vivo mechanism of cation transport are discussed.

² Present address: Department of Radiation Biology and Biophysics, The University of Rochester, School of Medicine and Dentistry, Rochester, N. Y. 14620.

Manuscript received 12 February 1970.