HIGH-CONCENTRATIONS OF ATRIAL-NATRIURETIC-PEPTIDE AND BRAIN NATRIURETIC PEPTIDE IN RAT PERICARDIAL FLUID AND THEIR REDUCTION BY RESERPINE IN-VIVO

We determined concentrations and molecular sizes of natriuretic peptid es in rat pericardial fluid and plasma by use of specific radioimmunoa ssays (RIA) and gel filtration HPLC. Our study shows that pericardial fluid forms a local extracellular storage of immunoreactive (ir) atria l natriuretic peptide (irANP) and brain natriuretic peptide (irBNP) ne ar the heart where these peptides can be found in high concentrations in vivo. The concentrations of irANP, irBNP and NH2-terminal fragment of proANP (irNT-proANP) in pericardial fluid were 9.8 +/- 3.7, 0.49 +/ - 0.47 and 28.9 +/- 11.8 nmol/l, respectively. IrBNP had the lowest (2 0 +/- 11) and irANP the highest (90 +/- 32) concentration ratio betwee n pericardial fluid and plasma. The elution positions of irANP, irBNP and irNT-proANP in pericardial fluid and plasma were similar as examin ed by gel filtration HPLC. Furthermore, we show that the reduction of noradrenaline content of the heart muscle by reserpine reduces concent ration of irANP in pericardial fluid by 39.6% and in plasma by 30.3% w hen compared to respective control group values. The concentration of irBNP is reduced by 44.1% in pericardial fluid but in plasma its reduc tion was not statistically significant. Vasoactive peptides released i nto the interstitial space and from there into pericardial fluid may h ave a more active role in the regulation of cardiac function than prev iously considered.