AJP - Heart and Circulatory Physiology, Vol 272, Issue 2 820-H826, Copyright © 1997 by American Physiological Society
Atrial systolic pressure, as well as stretch, is a principal stimulus for release of ANF
G. Christensen and E. Leistad
Institute for Experimental Medical Research and Research Forum, University of Oslo, Norway.
The mechanism for increased secretion of atrial natriuretic factor (ANF)
during tachycardia and atrial fibrillation has remained unsettled. In seven
open-chest pigs, the plasma concentration of ANF increased from 49.8 +/-
12.4 to 131.8 +/- 15.7 pg/ml when heart rate was increased from 133 +/- 13
to 212 +/- 4 beats/min by atrial pacing. Right atrial maximal diameter,
recorded by ultrasonic technique at the maximal atrial filling, did not
increase. During pacing tachycardia, the atrial contraction (a wave) occurs
during atrial filling, and the a wave becomes superimposed on the v wave.
In the present study the systolic atrial pressure (a wave) increased from
5.8 +/- 0.8 to 9.6 +/- 0.5 mmHg. The significance of this pressure rise was
subsequently examined. After complete atrioventricular (AV) block, the AV
delay was progressively increased, without altering heart rate, until the a
wave was similar to the the a wave during the preceding tachycardia. Plasma
ANF increased to 113.8 +/- 14.7 pg/ml, which showed that the increase in
atrial pressure during atrial systole is a stimulus for ANF release. In the
second part of the study, atrial fibrillation was induced in six open-chest
pigs by rapid atrial pacing after complete AV block. Plasma ANF increased
from 83.5 +/- 7.2 to 269.0 +/- 45.4 pg/ml during atrial fibrillation. No
increase in atrial dimensions occurred during atrial fibrillation, but
atrial pressure was substantially elevated. Thus, although passive atrial
stretch stimulates ANF release during blood volume expansion, the present
study shows that the increase in atrial pressure during atrial contraction
is a stimulus for release of ANF during tachycardia and atrial
fibrillation.
