The increase in glomerular filtration rate after a protein meal is believed to be mediated by hormonal factors. Since natriuresis is often observed after a protein meal, it was postulated that the increase in glomerular filtration rate after a protein meal might be mediated by atrial natriuretic peptide. 2. Subjects were given a low, medium or high protein meal. Fluid intake was controlled so as to avoid significant extracellular fluid volume expansion. It was found that the creatinine clearance, the urea excretion, the fractional sodium excretion and the potassium excretion were elevated in all subjects after protein meals (P less than 0.05). These effects were not observed in subjects given a carbohydrate control meal. 3. The plasma atrial natriuretic peptide concentrations remained unchanged in all subjects except those given a high protein meal (P less than 0.05). There was no significant relationship between plasma atrial natriuretic peptide concentrations and creatinine clearance before or after a protein meal. 4. The data suggest that a high protein meal induces a minor increase in plasma atrial natriuretic peptide concentration, whereas a low or medium protein meal does not. It is unlikely that the change in creatinine clearance after a protein meal can be explained by a change in plasma atrial natriuretic peptide levels.
