NONLINEAR-SYSTEM ANALYSIS OF RENAL AUTOREGULATION IN NORMOTENSIVE ANDHYPERTENSIVE RATS

We compared the dynamic characteristics in renal autoregulation of blo od flow of normotensive Sprague-Dawley rats (SDR) and spontaneously hy pertensive rats (SHR), using both linear and nonlinear systems analysi s. Linear analysis yielded only limited information about the differen ces in dynamics between SDR and SHR. The predictive ability, as determ ined by normalized mean-square errors (MMSE), of a third-order Volterr a model is better than for a linear model. This decrease in NMSE with a third-order model from that of a linear model is especially evident at frequencies below 0.2 Hz. Furthermore, NMSE are significantly highe r in SHR than SDR, suggesting a more complex nonlinear system in SHR. The contribution of the third-order kernel in describing the dynamics of renal autoregulation in arterial blood pressure and blood flow was found to be important. Moreover, we have identified the presence of no nlinear interactions between the oscillatory components of the myogeni c mechanism and tubuloglomerular feedback (TGF) at the level of whole kidney blood flow in SDR, An interaction between these two mechanisms had previously been revealed for SDR only at the single nephron level. However, nonlinear interactions between the myogenic and TGF mechanis ms are not detected for SHR.