PRESENCE OF C-TYPE NATRIURETIC PEPTIDE IN HUMAN KIDNEY AND URINE

The current study was undertaken to investigate the presence of CNP im munoreactivity in both human kidney and urine. Immunohistochemical sta ining with an indirect immunoperoxidase method utilizing an antibody w hich is 100% cross-reactive to both CNP-53 and CNP-22 was performed on five human kidney specimens (three biopsies of normal cadaveric donor kidneys and two of normal autopsy specimens). CNP immunoreactivity wa s positive in proximal, distal and medullary collecting duct tubular c ells in a cytoplasmic and granular staining pattern. CNP immunoreactiv ity was also determined in the urine of five healthy volunteers utiliz ing a sensitive and specific double-antibody radioimmunoassay with a m ean concentration of 10.8 +/- 1.0 pg/ml. With the utilization of high pressure liquid chromatography, this immunoreactivity proved to be con sistent with both the low molecular weight form, CNP-22, as well as th e high molecular weight form, CNP-53. Urinary excretion of CNP was als o measured in normal subjects (N = 5) and in patients with congestive heart failure (CHF, N = 6). CHF patients excreted over three times mor e CNP than normals (27.2 +/- 2.8 vs. 8.7 +/- 0.81 pg/min, P < 0.004) d espite no difference between the two groups in plasma CNP concentratio ns (6.97 +/- 0.28 vs. 8.08 +/- 1.52 pg/ml, P = NS). This study demonst rates for the first time the presence of CNP immunoreactivity in human kidney and suggests that renal tubular cells may be an additional non -vascular site of synthesis for this cardiorenal acting peptide. This study also demonstrates an increase in urinary CNP excretion in conges tive heart failure.