Dynamic analysis of renal nerve activity responses to baroreceptor denervation in hypertensive rats

Sinoaortic and cardiac baroreflexes exert important control over renal sympathetic nerve activity. Alterations in these reflex mechanisms contribute to renal sympathoexcitation in hypertension. Nonlinear dynamic analysis was used to examine the chaotic behavior of renal sympathetic nerve activity in normotensive Sprague-Dawley and Wistar-Kyoto rats and spontaneously hypertensive rats before and after complete baroreceptor denervation (sinoaortic and cardiac baroreceptor denervation). The peak interval sequence of synchronized renal sympathetic nerve discharge was extracted and used for analysis. In all rat strains, this yielded systems whose correlation dimensions converged to similar low values over the embedding dimension range of 10 to 15 and whose greatest Lyapunov exponents were positive. In Sprague-Dawley and Wistar-Kyoto rats, compete baroreceptor denervation was associated with decreases in the correlation dimensions (Sprague-Dawley: 2.42 +/-0.04 to 2.16 +/-0.04, Wistar-Kyoto: 2.44 +/-0.04 to 2.34 +/-0.04) and in the greatest Lyapunov exponents (Sprague-Dawley: 0.199 +/-0.004 to 0.130 +/-0.015; Wistar-Kyoto: 0.1961 +/-0.002 to 0.136 +/-0.010). Spontaneously hypertensive rats had a similar correlation dimension, which was unaffected by complete baroreceptor denervation (2.42 +/-0.02 versus 2.42 +/-0.03), and a lower value for the greatest Lyapunov exponent, which decreased to a lesser extent after complete baroreceptor denervation (0.183 +/-0.006 versus 0.158 +/-0.006). These results indicate that removal of sinoaortic and cardiac baroreceptor regulation of renal sympathetic nerve activity is associated with a greater decrease in the chaotic behavior of renal sympathetic nerve activity in normotensive compared with hypertensive rats. This suggests that the central neural mechanisms that regulate renal sympathetic nerve activity in response to alterations in cardiovascular reflex inputs are different in spontaneously hypertensive rats from those in Sprague-Dawley and Wistar-Kyoto rats.