Balance of net base in the rat. V. Effects of oral ammonium chloride loading

The physiology of oral ammonium chloride loading was studied in four groups of male weanling rats weighing about 100 g and fed either standard ground Rostock rat food (containing 317 mmol net base/kg) or ground barley (containing only 20 mmol net base/kg). One group of animals on the Rostock diet received oral supplements of ammonium chloride (approximately 32 mmol . kg-1 . day-1) sufficient to provide a net zero rate of oral net base intake. In this group, ongoing fecal net base excretion caused net acid to be absorbed at an average rate of 15 mmol . kg-1 . day-1. The mean rate of renal net acid excretion rose markedly (by 29.4 mmol . kg-1 . day-1); and over an 8-day balance period the animals were able to maintain near-normal balances of net base. During a subsequent 8-day recovery the pattern of mineral turnover returned to normal. Even in the barley-fed rats, gastrointestinal net acid absorption was observed. These animals suffered a 61% reduction in the rate of body growth, but the overall rate of net base retention, per kilogram of mass gain, was close to the reference value. Finally, the combination of barley and ammonium chloride led to weight loss, positive net acid balances (8.5 mmol . kg-1 . day-1), and a maximal rate of renal net acid excretion (50.8 mmol . kg-1 . day-1). Some implications for the metabolism of organic acids are discussed.