Effect of alpha- and beta-adrenergic stimulation on atrial natriuretic peptide release in vitro

The role of intracellular signals in the regulation of atrial natriuretic peptide (ANP) release was studied using the isolated left and right atria from a rat. The atria were perfused with Tyrode's solution, equilibrated with 95% O2-5% CO2 at 37 degrees C with a constant flow of 0.5 ml/min. Addition of epinephrine (10(-6) M), an alpha- and beta-agonist, to the perfusate induced the biphasic release of ANP from the right atrium without effect on the left. The initial peak (19.2 +/- 2.6 pg.min-1.ml-1) occurs 2-4 min after the administration of epinephrine, which lasted 4-6 min and returned to base line (10.4 +/- 1.1 pg.min-1.mg-1). The second peak (16.5 +/- 2.0 pg.min-1.ml-1) appeared 30-35 min after epinephrine administration and was sustained for 100 min, at which time the experiment was terminated. The first peak was stimulated by isoproterenol (10(-6) M), a beta-agonist, and blunted by propranolol (10(-6) M), a beta-antagonist. The second peak appeared following methoxamine (10(-6) M), an alpha-agonist, and could be suppressed by phentolamine (10(-6) M), an alpha-antagonist. These studies indirectly suggest that the adenosine 3',5'-cyclic monophosphate system and the inositol triphosphate system are involved in ANP secretion, with the former responsible for the initial rapid release and the latter maintaining the secretion.