Renin-angiotensin system (RAS) overactivity has been implied in progressive renal function loss. We investigated whether changes in the renal expression of RAS components are specifically associated with the proteinuric kidney.Unilateral adriamycin-induced proteinuria was obtained by clamping the left renal artery before injection of adriamycin. In control animals, both left and right renal arteries were clamped. Twelve weeks later, mRNA expression of RAS components was determined in both kidneys. In the affected and non-affected kidney of the unilateral proteinuric rat, we demonstrate up-regulation of angiotensin-converting enzyme (ACE) mRNA (213%±22 and 188%±24 of controls, respectively), up-regulation of transforming growth factor (TGF- ) mRNA (956%±229 and 418%±56) and down-regulation of angiotensin type 2 receptor (AT₂-R) mRNA (24%±5 and 20%±5). The expression of angiotensin type 1 receptor (AT₁-R) mRNA and inositol 1,4,5-trisphosphate receptor type I (IP₃R-I) mRNA were unchanged.In conclusion, renal expression of ACE, AT₂-R, and AT₁-R mRNA is not mediated by protein leakage. Local intrarenal protein leakage did influence renal TGF- mRNA expression.