OBJECTIVE To evaluate the effects of acute loading of protein from different sources on the glomerular filtration rate.

RESEARCH DESIGN AND METHODS A total of 6 healthy volunteer subjects and 6 diabetic patients with normoalbuminuria were studied before and after ingestion on separate days of tuna fish containing 0.7 g/kg body wt of protein, boiled egg white containing the same amount of protein as the tuna fish, or boiled egg white containing 1.4 g/kg body wt of protein. Furthermore, to study the possible role of prostaglandins and amino acids in the response of GFR to protein loading, urinary excretion of prostaglandins, and plasma levels of amino acids were measured during these tests.

RESULTS In normal subjects, the GFR rose significantly (P < 0.01) after ingestion of tuna fish. No significant differences were found between GFR before and after ingestion of the different amounts of egg white. The GFRs of the diabetic patients after ingestion of each of the meals were similar to the responses in healthy volunteers. Plasma levels of Gly and Ala (amino acids known to induce glomerular hyperfiltration) were higher after ingestion of tuna fish than after administration of egg white in all subjects. No differences were found in the plasma concentrations of any amino acids except Gly and Ala after loads of tuna fish and egg white containing 1.4 g/kg of protein. Urinary 6-keto-PGF_1a excretion increased significantly (P < 0.01) after tuna fish loading, but did not change after egg white challenge.

CONCLUSIONS These findings could be explained either by differences in renal vasodilatory prostaglandin secretion or by increased plasma levels of Gly and Ala, which were increased only after ingestion of tuna fish. Thus, egg white has renal effects on GFR different from those of tuna fish, independent of the quantity of protein ingested.