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Supplement: Second International Acid-Base Symposium, Nutrition–Health–Disease

Food Composition and Acid-Base Balance: Alimentary Alkali Depletion and Acid Load in Herbivores^1,2

³ Department of Physiology, Faculty of Medicine, Ruhr-University, 44780 Bochum, Germany; ⁴ Research Institute of Child Nutrition, 44225 Dortmund, Germany; and ⁵ Paediatric Clinic, 44137 Dortmund, Germany

^* To whom correspondence should be addressed. E-mail: heidrun.kiwull-schoene{at}rub.de.

Alkali-enriched diets are recommended for humans to diminish the net acid load of their usual diet. In contrast, herbivores have to deal with a high dietary alkali impact on acid-base balance. Here we explore the role of nutritional alkali in experimentally induced chronic metabolic acidosis. Data were collected from healthy male adult rabbits kept in metabolism cages to obtain 24-h urine and arterial blood samples. Randomized groups consumed rabbit diets ad libitum, providing sufficient energy but variable alkali load. One subgroup (n = 10) received high-alkali food and 15 mEq/kg ammonium chloride (NH₄Cl) with its drinking water for 5 d. Another group (n = 14) was fed low-alkali food for 5 d and given 4 mEq/kg NH₄Cl daily for the last 2 d. The wide range of alimentary acid-base load was significantly reflected by renal base excretion, but normal acid-base conditions were maintained in the arterial blood. In rabbits fed a high-alkali diet, the excreted alkaline urine (pH_u > 8.0) typically contained a large amount of precipitated carbonate, whereas in rabbits fed a low-alkali diet, both pH_u and precipitate decreased considerably. During high-alkali feeding, application of NH₄Cl likewise decreased pH_u, but arterial pH was still maintained with no indication of metabolic acidosis. During low-alkali feeding, a comparably small amount of added NH₄Cl further lowered pH_u and was accompanied by a significant systemic metabolic acidosis. We conclude that exhausted renal base-saving function by dietary alkali depletion is a prerequisite for growing susceptibility to NH₄Cl-induced chronic metabolic acidosis in the herbivore rabbit.