Urinary organic anion excretion in response to dietary acid and base loading

Animals eating a base-loaded or base-forming diet excrete urine containing large amounts of organic anions (OA). Although citrate is the only OA previously identified as being excreted in appreciable amounts during base loading, citrate excretion accounts for only part of total OA excretion. The objectives of this study were to identify other OA excreted by rats and to see how their excretion changed in response to moderate (8 micro Eq/g per day) and heavy (30 micro Eq/g per day) loads of NaHCO3 and NH4Cl. Urinary OA were identified by high-performance liquid chromatography and were measured by enzymatic techniques as well. It was found that, in addition to citrate, significant quantities of alpha-ketoglutarate (alpha-KG) were excreted by base-loaded rats and that the excretion of citrate, alpha-KG, and succinate increased with base loading and decreased with acid loading. Citrate plus alpha-KG excretion rates were, respectively, two-thirds and one-third the rate of HCO3- excretion in rats given moderate and heavy base loads. The excretion of creatinine, glutamine, and hippurate showed no clear pattern in response to acid or base loading. It was concluded that, especially in animals experiencing moderate base loads, increases in the excretion of citrate and alpha-KG represent a much more significant component of base excretion than has been recognized previously.