Effects of a low-sodium diet on electrolyte transport in the proximal and distal colon of the guinea pig (Cavia porcellus).

1. Animals were randomly assigned to three different treatment groups. (I) Control group maintained on a standard guinea pig diet, (II) a group obtaining a low-Na diet (0.02% Na w/w) and (III) a group fed the low-Na diet and in addition being treated with K-canrenoate prior to the perfusion experiment. 2. Proximal and distal colonic segments of anesthetized guinea pigs were perfused simultaneously with Ringer's solution. 3. In the proximal colon of the control group Na and Cl were absorbed in equal quantity and K was secreted. 4. In the distal colon of the control group Na and K were absorbed and Cl was secreted. Na absorption was only approximately 1/10 of that in the proximal colon. 5. Feeding a low-Na diet for two weeks induced secondary hyperaldosteronism. Plasma aldosterone concentration increased 3.4-fold. Na and Cl absorption rose 34% and 27% above control in the proximal colon, respectively. In the distal colon Na absorption was elevated 3.7-fold above control. 6. Na absorption and transepithelial potential difference (PD) in the proximal colon were amiloride-insensitive in all groups. In the distal colon Na absorption was abolished by luminal amiloride and the transepithelial PD was reversed in polarity. 7. K-canrenoate treatment prevented the increase in Na transport in the distal colon.