Sympathetic modulation of renal autoregulation by carotid occlusion in conscious dogs.

The effects of a moderate reflex activation of the sympathetic nervous system on renal blood flow (RBF) and glomerular filtration rate (GFR) were studied in 29 experiments on seven conscious foxhounds. Autoregulation parameters were derived by a stepwise reduction of renal artery pressure of 10-mmHg decrements. An occlusion of both common carotid arteries (CCO) was used as a moderate sympathetic stimulus. This procedure did not influence the basal levels of RBF and GFR. However, the lower limits of autoregulation were considerably shifted (RBF, control 63 +/- 3 mmHg vs. CCO 91 +/- 8 mmHg, P less than 0.01; GFR, control 77 +/- 5 mmHg vs. CCO 102 +/- 5 mmHg, P less than 0.01). CCO also affected the rate by which RBF and GFR decreased below the autoregulatory range (subautoregulatory function: RBF, control y = 0.056x - 1.4 vs. CCO y = 0.037x - 0.9 ml.mmHg-1.g-1, P less than 0.05; GFR, control y = 0.0089x - 0.4 vs. CCO y = 0.0054x - 0.28 ml.mmHg-1.g-1, P less than 0.05). An alpha-blockade via intrarenal prazosin infusions markedly inhibited these effects of CCO. These findings demonstrate the failure of autoregulation below 102 mmHg for GFR and 91 mmHg for RBF during sympathetic activation, and they may be of clinical importance for situations that are characterized by a high sympathetic tone.