Glomerular protein synthesis in proteinuric rats.

Intraperitoneal injection of bovine albumin in rats readily induces proteinuria. It is already known that this proteinuria is accompanied by ultrastructural and enzyme changes in the glomeruli. The purpose of the present study is to investigate whether these phenomena were associated with an increased glomerular protein synthesis or, more specifically, with an increased glomerular basement membrane (GBM) synthesis. Young rats were made proteinuric by the injection of bovine albumin. Their glomeruli were isolated by the sieve technique and incubater either with [U-14C]proline or with [U-14C]leucine and [U-14C]tyrosine. Control incubations were run with normal glomeruli. Glomerular proteins were hydrolyzed and analyzed for amino acid composition and radioactivity. Specific activities of all three amino acids were always higher in proteinuric glomeruli, but there was no difference in the ratio 14C-hydroxyproline/14C-proline. The similar increase in incorporation of the three amino acids must result from an increased synthesis of different cellular proteins and cannot be considered as a preferential increase in GBM synthesis.