Resetting of renal autoregulation in conscious dogs: angiotensin II and alpha1-adrenoceptors.

It has recently been shown, that common carotid occlusion (CCO) impairs autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR). This study was designed to investigate the mechanisms by which a moderate sympathetic stimulus influences RBF and GFR autoregulation. CCO provided a moderate sympathetic stimulus, and impaired autoregulation by increasing the lower autoregulatory limit of RBF and GFR by 21-30 mmHg. Basal RBF and GFR were not affected. A low-dose intrarenal infusion of the alpha 1-adrenoceptor agonist methoxamine (which did not change total RBF or GFR) induced a similar shift as CCO (n = 5, RBF: +31 +/- 11 mmHg, P less than 0.05; GFR: +24 +/- 4 mmHg, P less than 0.01). In another group it was shown, that a combination of CCO with an intrarenal angiotensin II (A II) blockade (saralasin) did not significantly alter the response to CCO (n = 7). These data suggest an alpha 1-adrenergic pathway for the sympathetic resetting of autoregulation. An augmented A II formation does not play a major role in mediating this effect.