Dynamic autoregulation in the in vitro perfused hydronephrotic rat kidney.
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 approximately 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.
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Division of Nephrology and Lady Davis Institute, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Loutzenhiser
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D000818:Animals; D001160:Arterioles / Q000502:physiology / Q000503:physiopathology; D001284:Atrophy; D005246:Feedback; D006706:Homeostasis; D006869:Hydronephrosis / Q000473:pathology / Q000503:physiopathology*; D066298:In Vitro Techniques; D007668:Kidney / Q000473:pathology / Q000502:physiology / Q000503:physiopathology*; D007678:Kidney Glomerulus / Q000502:physiology / Q000503:physiopathology; D007684:Kidney Tubules / Q000502:physiology / Q000503:physiopathology; D008297:Male; D008954:Models, Biological; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000502:physiology*; D014513:Ureter; D014661:Vasoconstriction