TUBULOGLOMERULAR FEEDBACK IN DAHL RATS

We have previously demonstrated a loss of autoregulation in Dahl salt- sensitive (Dahl-S) rats rendered hypertensive on a high-salt diet. To determine whether this was due to a decreased activity of either the m yogenic or the tubuloglomerular feedback (TGF) response, we tested the TGF response in both Dahl-S and salt-resistant Dahl rats on high- and low-salt diets. TGF was investigated in the closed-loop mode with a v ideometric technique, in which the response in late proximal flow rate to perturbations in Henle flow rate was measured. All Dahl rats showe d a similar compensatory response to perturbations around the natural operating point, with a TGF response that was more efficient than in n ormotensive Sprague-Dawley rats. No evidence of decreased TGF responsi veness in hypertensive Dahl-S rats was found. The results suggest that the loss of autoregulation in hypertensive Dahl-S rats is due to a co mpromised myogenic response. We also measured the free-flow proximal i ntratubular pressure in Dahl rats. Perfectly regular oscillations were demonstrated in all Dahl series, including the hypertensive Dahl-S ra ts. This is the first demonstration of regular oscillations in an expe rimental rat model of hypertension.