Possibility of age regulation of the natriuretic peptide C-receptor in human platelets

Natriuretic peptide binding sites on platelets have been hypothesized to ac t as clearance receptors; however, there is no clear definition of the func tion of this receptor. The aim of the study was: 1) to characterize natriur etic peptide receptors in human platelets by original competition study; 2) to evaluate a possible age modulation of these binding sites, since a dela yed clearance of ANP in the elderly has been observed. The binding of I-125 -ANP to intact platelets was completely inhibited by h-ANP, h-BNP, h-CNP an d c-ANP, the selective ligand of the clearance receptor. IC50 values were 0 .089+/-0.029, 0.703+/-0.104 and 1.19+/-0.13, 3.84+/-0.04 nmol/l, mean+/-SE, respectively (p<0.001 for IC50 value of h-ANP compared to the other natriu retic peptides). This observation on the receptor selectivity of natriureti c peptides in human platelets provides new evidence for the presence of the clearance receptor on platelets. In control subjects the K-d was 34.6+/-4. 0 pmol/l and B-max 13.6+/-0.92 fmol/10(9) platelets (mean+/-SE), (no.=46, m ean age 41.7+/-2.1 years). B-max was significantly reduced in older subject s (no.=25, mean age 53.2+/-1.5 years) with respect to the younger group (no .=21, mean age 28.0+/-0.87 years): 11.4+/-1.1 vs 16.1+/-1.4 fmol/10(9) cell s, p=0.0096, respectively; moreover, a significant inverse relationship bet ween Bmax and the subject's age was observed. This observation suggests a p ossible reduction of the natriuretic peptide clearance with aging, associat ed to a significant increase of plasma levels of natriuretic peptides. (C) 2001, Editrice Kurtis.