Contribution of baroreceptors and chemoreceptors to ventricular hypertrophy produced by sino-aortic denervation in rats

Abstract

1. To test whether sino-aortic denervation (SAD)-induced right ventricular hypertrophy (RVH) is a consequence of baroreceptor or chemoreceptor denervation, we compared the effects of aortic denervation (AD), carotid denervation (CD), SAD and a SAD procedure modified to spare the carotid chemoreceptors (mSAD), 6 weeks after denervation surgery in rats. A sham surgery group served as the control. 2. The blood pressure (BP) level was unaffected by AD, CD or SAD, but increased (9 %) following mSAD. The mean heart rate level was not affected. Short-term BP variability was elevated following AD (81 %), SAD (144 %) and mSAD (146 %), but not after CD. Baroreflex heart rate responses to phenylephrine were attenuated in all denervation groups. 3. Significant RVH occurred only following CD and SAD. These procedures also produced high mortality (CD and SAD) and significant increases in right ventricular pressures and haematocrit (CD). 4. Significant left ventricular hypertrophy occurred following CD, SAD and mSAD. Normalized left ventricular weight was significantly correlated with indices of BP variability. 5. These results suggest that SAD-induced RVH is a consequence of chemoreceptor, not baroreceptor, denervation. Our results also demonstrate that a mSAD procedure designed to spare the carotid chemoreceptors produced profound baroreflex dysfunction and significant left, but not right, ventricular hypertrophy.

Figure 1. Mean blood pressure (BP) levels among the five groups, 6 weeks after surgery

The mean BP represents the mean of 5760 samples obtained at 30 s intervals over a 48 h period using BP telemetry. ○, individual data points; ♦, group means. The interrupted line indicates the mean BP level in the sham group. * Significantly different from the sham group.

Figure 2. Short-term blood pressure (BP) variability among the five groups, 6 weeks after surgery

The short-term BP variability was calculated as the average standard deviation of BP values within 96 individual half-hour periods over the course of a 48 h recording. The interrupted line indicates the mean level of short-term BP variability in the sham group. * Significantly different from the sham group.

Figure 3. Peak blood pressure (BP) level in the five groups, 6 weeks after surgery

The peak BP level was determined as the BP level corresponding to the top 1 percentile of 5760 BP samples obtained over a 48 h period. ○, individual data points; ♦, group means. The interrupted line indicates the mean peak BP level of the sham group. * Significantly different from the sham groups.

Figure 4. Left ventricular weights in the five groups, 6 weeks after surgery

The weights are normalized to body weight. ○, individual data points; ♦, group means. The interrupted line indicates the mean left ventricular weight in the sham group. n = 21, 17, 18, 17 and 14 in the Sham, AD, mSAD, SAD and CD groups, respectively. * Significantly different from the sham group.

Figure 5. Right ventricular weights in the five groups, 6 weeks after surgery

The weights are normalized to body weight. ○, individual data points; ♦, group means. The interrupted line indicates the mean right ventricular weight in the sham group. n = 21, 17, 18, 17 and 14 in the Sham, AD, mSAD, SAD and CD groups, respectively. * Significantly different from the sham groups.

Figure 6. Scatter plots showing the relationship between left ventricular weight (LVW) and mean blood pressure level (mean BP), the daily peak BP level (peak BP) and the short-term blood pressure variability (BPV)

Data from the sham (□), AD (♦) and mSAD (•) groups are included (n = 56). The continuous lines represent the regression line for each scatter plot. The regression equations were: LVW = 0.007 mean BP + 1.75 (P = 0.19, r = 0.18), LVW = 0.008 peak BP + 1.4 (P = 0.001, r = 0.42), and LVW = 0.03 BPV + 2.2 (P = 0.001, r = 0.44).