Dynamic autoregulation in the in vitro perfused hydronephrotic rat kidney

Abstract

Renal autoregulation is mediated by tubuloglomerular feedback, operating 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 this study, we examined dynamic autoregulation in the hydronephrotic rat kidney, which lacks tubuloglomerular feedback but exhibits pressure-induced afferent arteriolar vasoconstriction. Kidneys were harvested under anesthesia from Sprague-Dawley rats and perfused in vitro using defined, colloid-free medium. Renal perfusate flow was assessed during forced pressure fluctuations at mean pressures of 60–140 mmHg. Transfer function analysis revealed passive behavior at 60 mmHg and active, pressure-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 resonance peak in admittance gain at ≈0.3 Hz and an associated broad peak in phase angle. Below this frequency, gain declined progressively. The minimum gain achieved at 0.01–0.05 Hz was pressure sensitive, being 1.08 ± 0.02 at 60 mmHg and 0.71 ± 0.04 at 140 mmHg. These findings are consistent with in vivo results and with model-based predictions of the dynamics of myogenic autoregulation, supporting the postulate that the rapid component of autoregulation reflects operation of a myogenic mechanism.