Renal sympathetic nerve responses to somato-sensory nerve stimulation in normotensive rats

Blood pressure, heart rate and renal sympathetic nerve activity were recorded in groups of chloralose/urethane-anaesthetised intact, vagotomised and carotid sinus denervated Wistar rats before and during bilateral somatic afferent nerve stimulation from 0.1 to 3.2 Hz. Renal sympathetic nerve activity was subjected to power spectral and cross correlation analysis. Haemodynamic and integrated renal nerve responses to graded brachial nerve stimulation were not altered by either bilateral vagotomy or carotid sinus denervation and total power of the spectra, from 0-10 Hz, was similar in each group. The percentage power peak at heart rate in intact rats decreased with increasing stimulus frequency, from a control value of 19.2 +/- 1.9% to a minimum of 2.8 +/- 0.7% at 1.6 Hz, while coherence and phase were not altered. Conversely, the peak at the stimulus frequency rose with increasing stimulus frequency reaching 35.3 +/- 2.0% at 3.2 Hz. In the vagotomised group, power at heart rate was significantly lower at each stimulus frequency compared to intact rats although coherence was similar and the phase difference was larger. The peak power at stimulus frequency, coherence and phase difference were similar to those obtained in the intact rats. In the carotid sinus denervated rats, the percentage power at heart rate, coherence and phase difference were significantly smaller than in intact rats. The peak at the stimulus frequency and the phase difference were similar to those obtained in the intact rats whereas coherence was lower. These findings demonstrate that the pattern of renal nerve activity can be changed from one modulated by the baroreceptor to one driven by somatic afferent nerve activity. The vagus appears to play a minor role in the overall pattern of renal nerve activity with the primary controller being the carotid sinus baroreceptors. The data also show that the renal nerve response to somatic afferent nerve stimulation is independent of the afferent nerve input arising from either the atrial or the carotid sinuses.