DYNAMIC AUTOREGULATION AND RENAL INJURY IN DAHL RATS

The Dahl salt-sensitive (Dahl S) rat develops hypertension and renal i njuries when challenged with a high salt diet and has been considered to be a model of chronic renal failure. Renal injuries appear very ear ly in life compared with the spontaneously hypertensive rat (SHR). Dur ing the course of hypertension, a gradual impairment of autoregulatory control of renal blood flow might expose the glomerular circulation t o periods of elevated pressure, resulting in renal injuries in Dahl S rats. Dynamic autoregulatory capacity was assessed in Dahl S and Dahl salt-resistant (Dahl R) rats, SHR, and Sprague-Dawley rats by inducing broad-band fluctuations in the arterial blood pressure and simultaneo usly measuring renal blood flow. Dynamic autoregulation was estimated by the transfer function using blood pressure as the input and renal b lood flow as the output. Renal morphological injuries were evaluated i n Dahl S rats and SHR and were scored semiquantitatively. Dynamic auto regulation was efficient and comparable in the low-frequency range (<0 .015 Hz) in Dahl R rats, SHR, and Sprague-Dawley rats. The response in Dahl S rats depended strongly on the initiation time of the high salt diet. Autoregulation was preserved during a low salt diet and in rats exposed to a late-onset hypertension of short duration, only partly p reserved if the late-onset hypertension was of a longer duration, and abolished in early-onset hypertension. All Dahl S rats on a high salt diet showed severe morphological changes in the kidney. In conclusion, autoregulatory capacity in the kidney of Dahl S rats is gradually imp aired when rats are rendered hypertensive with a high salt diet. Renal morphological injuries develop before loss of dynamic autoregulation. Impaired autoregulation appears to be the result, not the cause, of t he process that ultimately leads to renal failure in the Dahl S rat.