Autoregulation of renal blood flow and blood pressure variability in the conscious rat

It is often proposed that autoregulatory mechanisms prevent acute changes i n systemic blood pressure (BP) from being transmitted to the glomerular cap illary circulation. However, it is not known whether renal blood flow (RBF) is still autoregulated when the kidney is exposed to exaggerated BP fluctu ations, in particular hypertensive episodes. The aim of the present study w as therefore to evaluate the efficacy of renal autoregulatory responses in an animal model of BP lability, the sinoaortic denervated (SAD) rat. BP and RBF were simultaneously recorded in 8 SAD (2 wks before study) and 8 baror eceptor intact (INT) Sprague-Dawley rats during similar to3 h of spontaneou s activity. The left kidney used for RBF recordings was denervated to preve nt the interference of changes in renal sympathetic tone with autoregulator y responses. The SAD procedure modified neither the mean BP nor the mean RB F levels (111 +/-1 mmHg and 11.3 +/-1.3 mL/min in INT rats; 113 +/-6 mmHg a nd 11.1 +/-0.9 mL/min in SAD rats). However, SAD strongly increased the BP variability (coefficient of variation: 5.9 +/-0.2% and 18.2 +/-1.1% in INT and SAD rats, respectively). In spite of this marked BP lability, RBF varia bility was not significantly affected by the SAD procedure (9.1 +/-0.8% and 12.4 +/-1.6% in INT and SAD rats, respectively). In SAD rats. spontaneous hypertensive episodes (top 1% of BP values: 174 +/- 10 mmHg) did not induce increases in RBF (10.5 +/-1.0 ml/min). Fast Fourier transform analysis rev ealed that in SAD rats. autoregulatory mechanisms attenuated approximately 80% of BP fluctuations in the 0.0015-0.01 Hz frequency range, suggesting a major involvement of the tubuloglomerular feedback. In conclusion, autoregulatory mechanisms have an ample capacity to protect the kidney against spontaneous BP fluctuations in the conscious rat. Conseq uently, BP variability per se is probably not detrimental to the kidney, as long as autoregulatory mechanisms are normally functioning.