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A new technique to permit gradual changes in atrial distension has been developed in an isolated perfused rabbit atrium preparation. Graded volume reduction in the atrium was induced by changing the elevation of the outflow catheter tip. Pressure reduction from 6 cm H2O atrial distension resulted in a decrease in atrial distension volume. Atrial distension by 6cmH2O did not change the release of immunoreactive atrial natriuretic peptide (irANP). The graded reduction in atrial distension from 0.11 ± 0.03 (1.5 cm H2O) to 1.36 ± 0.19µl/mg wet weight (6.0cm H2O) resulted in 1.7 (6.76 ± 2.05 versus 3.83 ± 1.18pg/mg per min, n=9, P< 0.025) to 40.1-fold (77.66 ±17.82 versus 3.0 ± 1.14pg/mg per min, n=11, P<0.025) increases in irANP relese.IrANP release in response to the reduction of atrial distension was volume dependent. The relation of percentage increase in irANP release with the percentage reduction of a trial distension was exponential. The data suggest that the atrial muscle shortening, but not stretch per se, may be a potent direct stimulus for the regulation of irANP secretion.