Arterial baroreflex dynamics in normotensive and spontaneously hypertensive rats

To investigate dynamic or frequency-dependent characteristics of arterial baroreflex control of efferent sympathetic nerve activity in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY), we assessed the transfer function from aortic pressure (AP) to renal sympathetic nerve activity (RSNA) using a "white-noise technique." In pentobarbital sodium-anesthetized rats, we recorded RSNA as the output, while AP was randomly perturbed to impose input pressure changes with broad frequencies. We calculated the transfer function from AP to RSNA over the frequency range of 0.01-5 Hz through the spectral analysis of the input and output. The results indicated that the gain, phase shift, and coherence of the transfer function for SHR and for WKY were similar and statistically indistinguishable. The gain was relatively constant below 0.05 Hz but increased steadily by fivefold as frequency increased in the frequency range of 0.05-0.8 Hz. The phase was out of phase where coherence was high. The coherence was high (greater than 0.5) in the frequency range of 0.04-0.8 and 1.00-1.03 Hz but was low in other frequencies. These results suggest that dynamic or frequency-dependent characteristics of arterial baroreflex control of RSNA were not altered in SHR as compared with WKY.