A method to evaluate renal ammoniagenesis in vivo.

A reduced rate of excretion of ammonium (NH4+) can be due to either a low rate of production and/or a low transfer of NH4+ to the urine. At present, there is no way to obtain a measure of the rate of production of NH4+ in vivo without invasive techniques. Hence, our purpose was to develop a non-invasive test to reflect this rate in vivo. Conditions were selected so that there would be a wide range in the rate of production of NH4+ in the kidney. Initial experiments were performed in dogs because both the rate of production and excretion of NH4+ could be measured directly. The rate of excretion of NH4+ in normal dogs on their usual diet varied over a wide range and was not directly related to its rate of production. Nevertheless, 59% of the NH4+ produced was excreted when the pH of urine was < 6 or when the rate of flow of urine was high (after administering a loop diuretic). To produce a urine with a low pH and high flow rate in humans, a loop diuretic (20 mg of furosemide) and a mineralocorticoid (200 micrograms of fludrocortisone) were given. The pH of urine fell to 5.1 and the rate of urine flow rose to 8 ml/min; the rate of excretion of NH4+ rose from 21 to 33 mumol/min when the urine flow rate rose.(ABSTRACT TRUNCATED AT 250 WORDS)