Evidence for C-type natriuretic peptide production in the rat kidney

To elucidate the physiological role of C-type natriuretic peptide (CNP) as a local mediator, we examined the production of CNP in the rat kidney. The content of CNP in the kidney was 0.47 +/- 0.02 [SE] fmol/mg wet weight and the major molecular form of CNP was CNP-53. An established cell line from the rat kidney, NRK-52E cell, secreted CNP at a rate of 9.15 +/- 0.96 fmol/24 hr/mg protein. Furthermore, CNP mRNA was detected in the rat kidney and NRK-52E cell utilizing reverse transcription-polymerase chain reaction (RT-PCR). On the other hand, ANP in the rat kidney (2.56 +/- 0.19 fmol/mg wet weight) had the molecular form of alpha-ANP, but ANP mRNA was not detected by RT-PCR. No BNP immunoreactivity was found in the rat kidney, although BNP mRNA was detected by RT-PCR. These results indicate that only CNP among the natriuretic peptides is produced in significant amounts in the rat kidney under normal physiological conditions and that renal parenchymal cells may produce CNP.