In vitro release of immunoreactive atrial natriuretic peptide from the rat atria

In vitro release of atrial natriuretic peptide (ANP) from atria was examined by ANP radioimmunoassay. Isolated right rat atria were incubated in Krebs-Ringer bicarbonate buffer, and test substances were added to the incubation medium. The fluid was assayed for rat ANP by a radioimmunoassay method recently developed in our laboratory. We produced an antiserum to human ANP(99-216) (alpha-hANP(1-28)) which showed a good cross-reactivity of 63% with rat ANP(99-126) (alpha-rANP(1-28)) and was useful for measuring rat ANP concentrations of the medium. Application of the medium to a reverse phase high performance liquid chromatography (HPLC) system resulted in a single peak of immunoreactive rat ANP corresponding to a small molecular weight synthetic rat ANP of 28 amino acid residues. Catecholamines (epinephrine, norepinephrine and isoproterenol) reduced the basal secretion of ANP, whereas acetylcholine stimulated the release of ANP. Forskolin and dibutyryl cyclic AMP did not affect the release of ANP. These results suggest the possibility that the regulation of ANP release may be partially associated with adrenergic and cholinergic mechanisms.