MECHANICAL BASIS OF ANP SECRETION IN BEATING ATRIA - ATRIAL STROKE VOLUME AND ECF TRANSLOCATION

To investigate the mechanism by which an increase in pacing frequency or distension increases the secretion of atrial natriuretic peptide (A NP), the changes in atrial volume during contraction (atrial stroke vo lume), transmural transport of the extracellular fluid (ECF), and ANP secretion were quantified in the beating perfused rabbit atria. The at rium was stimulated by transmural field stimulation or by atrial diste nsion induced by an increase in intraatrial pressure. Atrial stretch a nd incremental increases in pacing frequency up to 2 Hz activated the secretion of ANP coincident with an increase in atrial stroke volume a nd the transendocardial translocation of the ECF. These results showed positive relationships between changes in the secretion of ANP and th e atrial stroke volume or the translocation of the ECF. The translocat ion of the ECF was also positively correlated with the change in atria l stroke volume. The accentuated secretion of ANP and translocation of the ECF waned at higher stimulating rates to show a peak value. Even under this condition, the secretion of ANP was a function of the trans location of the ECF. These data suggest that the increases in atrial s troke volume and translocation of the ECF are fundamental factors in t he ANP stimulation in response to atrial stretch and increases in atri al rate.