EFFECT OF CHRONIC MITRAL-VALVE DAMAGE ON ACTIVITY OF PULMONARY RAPIDLY ADAPTING RECEPTORS IN THE RABBIT

1. The effects of acute pulmonary venous congestion on the activity of rapidly adapting receptors (RARs) were determined in intact (control and sham-operated) rabbits and in rabbits 6 and 12 weeks after surgica l destruction of the mitral valve. 2. Destruction of the mitral valve increased the mean left atrial pressure (LAP) by approximately 2.6 and 3.8 mmHg, 6 and 12 weeks after surgery respectively These changes wer e accompanied by significant increases in left ventricular weight. The effect of acute increments in LAP on RAR activity was examined agains t this background of chronic pulmonary venous congestion. 3. In intact control and sham-operated animals RAR activity increased from 48.8 +/ - 0.9 to 83.5 +/- 3.6 and 121.1 +/- 4.7 action potentials min(-1) when the LAP was raised by 5 and 10 mmHg, respectively above control value s. Six weeks after surgery only 40% of RARs were activated in this way . 4. In animals maintained for 12 weeks after surgery, RAR activity at LAPs of 6.6 +/- 1.2 (control), 11.6 +/- 1.2 and 16.6 +/- 1.2 (mmHg) w ere 35.5 +/- 2.3, 33.8 +/- 14.4 and 34.0 +/- 3.4 action potentials min (-1) respectively. These changes were statistically not significant. 5 . Slowly adapting receptors (SARs) in the lung showed a small but stat istically significant increase in activity when the left atrial pressu re was acutely elevated in both intact and mitral valve damaged animal s. 6. It is concluded that chronic pulmonary venous congestion resulti ng from destruction of the mitral valve attenuates the ability of RARs to respond to acute moderate elevations of LAP.