DYNAMIC AUTOREGULATION IN THE IN-VITRO PERFUSED HYDRONEPHROTIC RAT-KIDNEY

Renal autoregulation is mediated by tubuloglomerular feedback, operati ng at 0.03-0.05 Hz, and a faster system, operating at 0.1-0.2 Hz, that has been attributed by exclusion to myogenic vasoconstriction. In thi s study, we examined dynamic autoregulation in the hydronephrotic rat kidney, which lacks tubuloglomerular feedback but exhibits pressure-in duced afferent arteriolar vasoconstriction. Kidneys were harvested und er anesthesia from Sprague-Dawley rats and perfused in vitro using def ined, colloid-free medium. Renal perfusate flow was assessed during fo rced pressure fluctuations at mean pressures of 60-140 mmHg. Transfer function analysis revealed passive behavior at 60 mmHg and active, pre ssure-dependent responses at higher pressures. In all cases, coherence was high (0.89 +/- 0.03 between 0.01 and 0.9 Hz). There was a resonan ce peak in admittance gain at approximate to 0.3 Hz and an associated broad peak in phase angle. Below this frequency, gain declined progres sively. The minimum gain achieved at 0.01-0.05 Hz was pressure sensiti ve, being 1.08 +/- 0.02 at 60 mmHg and 0.71 +/- 0.04 at 140 mmHg. Thes e findings are consistent with in vivo results and with model-based pr edictions of the dynamics of myogenic autoregulation, supporting the p ostulate that the rapid component of autoregulation reflects operation of a myogenic mechanism.