INFLUENCE OF THE RENAL ENDOTHELIN-A SYSTEM ON THE AUTOREGULATION OF RENAL HEMODYNAMICS IN SHRS AND WKY RATS

In this study, we investigated the influence of a short-term blockade of the renal endothelin A system on the autoregulation of total renal blood flow, cortical renal blood flow, and pressure-dependent plasma r enin activity in spontaneously hypertensive rats (SHRs) and normotensi ve controls [Wistar-Kyoto (WKY) rats]. In anesthetized rats, renal blo od flow was measured by a transit-time flow probe and cortical blood f low by a laser flow probe. Blood samples were taken for measurement of plasma renin activity. Renal perfusion pressure was reduced in 5-mm H g steps by means of a servocontrolled electropneumatic device by an in flatable suprarenal cuff. During the experiments, the rats (n = 6, eac h group) received an intrarenal infusion of either the selective endot helin A-receptor antagonist BQ123 (3 mg/kg/h) or vehicle. We observed an improvement of total and cortical blood flow autoregulation as indi cated by a shift of lower limits of autoregulation to lower threshold pressures [103 +/- 2 vs. 132 +/- 4 mm Hg compared with 98 +/- 3 vs. 12 0 +/- 4 mm Hg (mean +/- SEM); p < 0.01 resp. p < 0.05] in BQ123-treate d SHRs, whereas BQ123 had no influence on breakpoints of autoregulatio n in WKY rats (p > 0.05). Pressure-dependent plasma renin activity in SHRs was not influenced by BQ123. Renal blood flow autoregulation is i mproved in SHRs after short-term blockade of the renal endothelin A sy stem. This effect is independent of the renin-angiotensin system. The endothelin A system does not seem to play an important role in the aut oregulation of renal blood flow in normotensive WKY rats.