STUDIES OF DYNAMICS OF PRESSURE INDUCED CHANGES OF FLOW RESISTANCE IN ISOLATED RAT KIDNEY

Using the isolated artifically perfused rat kidney the relationship between perfusion pressure and flow has been studied. Applying defined changes of pressure the resulting flow patterns were analyzed for changes of form, amplitude and phase. The following input patterns were used: 1. Rectangular pressure changes (step functions), and 2. sinusoidal pressure changes of frequencies between 0.0065 and 1.0 Hz. If the maximum pressure-in the experiments with step functions-does not exceed 100 mm Hg the transient response is proportional to the input changes. Step functions of a maximum pressure above 100 mm Hg induce characteristic distortions of the response curve. Upon addition of papaverin to the perfusion fluid these distortions disappear. With sinusoidal pressure changes a maximum of distortion of the response curve is obtained at a frequency of 0.06 Hz. The amplitude of the response reaches a maximum at 0.3 Hz and goes through a minimum at 0.02 Hz. Papaverin abolishes the distortions as well as the maximum and minimum of the flow amplitude. Addition to the perfusion fluid of the sympathicolytic substances Regitin or Dibenamine induces characteristic changes of the output pattern following step functions. In experiments where sinusoidal input functions were used the sympathicolytic substances abolish the distortions at 0.06 Hz, while the maximum of amplitude at 0.3 Hz is unaffected and the minimum at 0.02 Hz disappears. The results indicate that the reactive increase of flow-resistance in the autoregulating kidney is due to at least two mechanisms. With Regitin or Dibenamine an initial, short lasting, rate sensitive reactive component having a short latency and reaction time (0.3-0.7 sec) can be distinguished from a second, rate independent, long lasting component which has a longer reaction time (5-10 sec). © 1968 Springer-Verlag.