Abstract 15898: Lognormal Distribution of Sympathetic Nerve Activity in Normotensive and Spontaneously Hypertensive Rats
Purpose: Although multifiber recording of the sympathetic nerve is commonly used to assess sympathetic nerve activity (SNA) in animal studies, little is known as to the nature of its amplitude distribution. The amplitude distribution may provide a clue to understand the central processing to generate SNA. The present study compared the amplitude distribution of SNA between normotensive Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).
Methods: Under anesthetized conditions, multifiber SNA was recorded from a postganglionic branch of the splanchnic sympathetic nerve, and was digitized at 200 Hz after rectifying and low-pass filtering with a cut-off frequency of 30 Hz. The mean level of SNA was altered by varying isolated carotid sinus pressure from 60 to 180 mmHg (WKY, n=8) or 60 to 220 mmHg (SHR, n=8). At each input level, the SNA amplitude histogram was constructed over 60 s. In each animal, SNA was normalized based on the value corresponding to the 99th percentile of SNA observed at the input level of 60 mmHg.
Results: The SNA amplitude distribution approximated a lognormal distribution in both WKY and SHR, i.e., SNA had a distribution in the form of X = exp(μ +σZ) where μ and σ represent the scale parameter and shape parameter, respectively. Z is a variable with a standard normal distribution. The shape parameter did not differ between WKY (0.63±0.02) and SHR (0.58±0.03) at the input level of 60 mmHg, and did not vary significantly with changes in the input level. The scale parameter did not differ at 60 mmHg but was significantly greater in SHR at the input level of 80 mmHg and above, suggesting higher sympathetic tone in SHR.
Conclusion: The SNA amplitude distribution approximated a lognormal distribution irrespective of the input pressure level in both WKY and SHR. Because the lognormal distribution is seen as a result of multiplicative product of random variables, the baroreflex may control SNA in a manner to scale the signal rather than to modify its offset level.
- © 2012 by American Heart Association, Inc.