Circulating Immunoreactive proANP(1-30) and proANP(31-67) in Sedentary Subjects and Athletes

BACKGROUND: Atrial natriuretic peptide (ANP) is synthesized and stored in myocytes as prohormone(1-126), which upon release is cleaved into proANP(1-98) and alpha-ANP(99-126). In addition, cleavage of proANP(1-98) produces proANP(1-30), proANP(31-67), and proANP(79-98) fragments. ProANP(1-30) and proANP(31-67) have roles in fluid and electrolyte homeostasis. The aim of the present study was to develop a plasma assay for proANP(1-30) and proANP(31-67) and to compare results in trained athletes and sedentary subjects. METHODS: Two competitive enzyme immunoassays were established with affinity-purified sheep antiserum against synthetic ANP fragments. The immunoreactivity (ir) of proANP(1-30) and proANP(31-67) was measured in 10-microL plasma samples without extraction in a microwell-based assay. Plasma concentrations in sedentary male subjects (n = 22) and male endurance athletes (n = 14) were examined. RESULTS: In the assay for ir-proANP(1-30) and ir-proANP(31-67), the concentrations at 95% B/B(0) were 4.7 and 14.2 pmol/L, respectively. Within-run CVs were 4-6% and 5-6%, and between-run CVs were 9% for both assays. Both assays were linear on dilution (y = 0.9945x - 0. 7291 and y = 1.0001x - 3.428), and the recoveries were 102-112% and 102-106%, respectively. In the sedentary and athletic groups, the ir-proANP(1-30) concentrations were similar: 318 +/- 38 pmol/L and 312 +/- 25 pmol/L (mean +/- SE), respectively, whereas the ir-proANP(31-67) was higher in the rowers (713 +/- 81 pmol/L) than in the sedentary subjects (387 +/- 71 pmol/L; P <0.005). CONCLUSIONS: The proANP fragment assays are precise (CV <10%) and exhibit nearly quantitative recovery (102-112%). Only ir-proANP(31-67) responds to physical training.