Atrial wall function and plasma atriopeptin during volume expansion in conscious dogs

Mean left atrial pressure is believed to be an accurate estimate of atrial stretch in vivo and is used to assess the stimulus for atriopeptin release in both animals and humans. However, for a number of years it has been known that atrial stretch receptor discharge occurs during specific phases of the atrial cycle and that B-receptor discharge correlates with the passive filling of the atrium, which occurs during the V wave. The purpose of this study was to develop the concept that phase-specific changes in atrial wall stress are responsible for atriopeptin secretion. In chronically instrumented conscious dogs, volume expansion (1,000 ml of saline in 5 min) increased left atrial pressure and dimensions and caused a 663 +/- 189% increase in plasma immunoreactive atriopeptin from 44 pg/ml. At this time, mean left atrial pressure increased only 202 +/- 36% (mean +/- SE), whereas A wave pressure increased 146 +/- 19% and V wave pressure increased 290 +/- 67%. A and V wave dimensions increased only a few percent. After developing atrial wall thickness constants for diastole (KCl fixation) and systole (BaCl2 fixation), calculated atrial A wave wall stress increased 163 +/- 25%, and V wave wall stress increased 346 +/- 85%. Minute wall stress (wall stress times heart rate) gave an even better correlation with changes in plasma atriopeptin. V wave minute wall stress increased 690 +/- 168%, whereas A wave wall stress increased 366 +/- 56%.(ABSTRACT TRUNCATED AT 250 WORDS)