Tubulo-glomerular feedback response: enhancement in adult spontaneously hypertensive rats and effects of anaesthetics.

Open-loop tubulo-glomerular feedback (TGF) responses were measured in halothane anaesthetized spontaneously hypertensive rats (SHR), in normotensive Wistar Kyoto (WKY) and Sprague-Dawley rats (SPRD), and in inactin anaesthetized SPRD. Proximal intratubular free flow pressures (FFP) (13.8-14.7 mm Hg) and stop-flow pressures (40.0-42.4 mm Hg) were similar in the four groups, but systemic arterial pressure was significantly lower in WKY, and significantly higher in SHR than in SPRD. The turning point (Tp) of the feedback curve was 9.87 nl/min in SHR, significantly lower than the 13.04 nl/min found in WKY. Maximum TGF pressure response was 28.6% greater in SHR than in the normotensive rats (13.3 vs. 9.5 mm Hg; p less than 0.025). The sensitivity, as estimated from the slope of the feedback curve at the Tp [f'(Tp)] was 87% greater in SHR than in WKY. There was no significant difference between these parameters in WKY and SPRD. The TGF pressure response was biphasic in the 3 groups of halothane anaesthetized rats with a steady state level reached in about 2 min after the change in late proximal microperfusion rate. In inactin anaesthetized rats the sensitivity was 41% lower than in the halothane anaesthetized control group of SPRD, the feedback response was lower, and the feedback curve was displaced to the right with the Tp at 15.9 nl/min, significantly higher than in the control group (p less than 0.001). Although the steady state level also was reached within 2 min, the clearly biphasic pattern of the pressure response was less consistent.