A new method for kidney perfusion in situ: application to dynamics of autoregulation

A procedure for in situ perfusion of kidney was developed in which renal resistance does not rise with continued perfusion at a constant rate and renal blood flow (RBF) can be changed as a step function. The kidney of dogs anesthetized with pentobarbital-chloralose was perfused by a pulsatile syringe pump via an extracorporeal circuit placed between the femoral artery and the renal artery. The perfusion pressure and pulse rate can be adjusted to match those of the dog. Following a step change in RBF from the control level, the dynamics of the autoregulatory response was studied by determining the time course of the alteration in renal perfusion pressure as RBF was maintained at the new constant level. An increase in RBF led to a time-dependent renal vasoconstriction (increase in renal resistance), and a decrease in RBF caused a time-dependent renal vasodilation (decrease in renal resistance). The time course of the response of renal resistance to step changes in RBF can be described by monoexponential functions. The time constant obtained for resistance changes after both an increase and a decrease in RBF was 37.5 +/- 2.8 (SD) s. During the period of step recovery from changes in RBF in either direction, the time constant of the renal resistance response was 53.4 +/- 3.2 s. These values are useful for the analysis of the mechanism of renal autoregulation as well as the modeling of circulatory and hormonal control. The results also indicate that this new procedure for renal perfusion in situ is well suited for studying renal hemodynamics and other functions.