Natriuretic peptide B receptor and C-type natriuretic peptide in the rat kidney

Natriuretic peptide receptor B (ANP-RGC(B)) has been previously identified in the kidney. It binds C-type natriuretic peptide (CNP) with high affinity and the two other natriuretic peptides (atrial natriuretic peptide and brain natriuretic peptide) with low affinity, and mediates the biological effects of CNP. The purpose of this investigation was to identify sites of ANP-RGC(B) mRNA in the rat renal tubule and to confirm that CNP itself is synthesized in the rat kidney. Kidneys from male Sprague-Dawley rats were removed and divided into cortex, outer medulla, and inner medulla. Using reverse transcriptase and polymerase chain reaction techniques, ANP-RGC(B) mRNA was identified in the three principal regions of the kidney. Individual glomeruli and segments of the renal tubule were microdissected and subjected to reverse transcriptase-polymerase chain reaction. ANP-RGC(B) mRNA was regularly found (>60% of animals) in glomeruli, distal convoluted tubule, and cortical, outer medullary, and inner medullary tubules but not in the proximal convoluted tubule, proximal straight tubule, thin or medullary thick ascending limb. ANP-RGC(B) mRNA was also identified in outer medullary descending vasa recta. Glyceraldehyde-3-phosphate-dehydrogenase and natriuretic peptide A receptor mRNA were present in all segments. In a separate study, CNP mRNA was identified in whole kidney, cortex, and medulla. These findings confirm that CNP and its receptor are present in the rat kidney. The proximity of the ligand and receptor suggests that CNP may have paracrine or autocrine regulatory functions in the rat kidney.