Baroreflex sympathetic activation increases threshold pressure for the pressure-dependent renin release in conscious...

Stimulus-response curves relating renal-venous-arterial plasma renin activity difference (P.R.A.-difference) to mean renal artery pressure (R.A.P.) were studied in seven chronically instrumented conscious foxhounds with a daily sodium intake of 6.1 mmol/kg. R.A.P. was reduced in steps and maintained constant for 5 min using an inflatable renal artery cuff and a pressure control system. The stimulus-response curve obtained during control conditions (C) or during common carotid artery occlusion (C.C.O.) could be approximated by two linear sections: a rather flat section or plateau-level of P.R.A.-difference at normal blood pressure or above, and a very steep section between a distinct threshold pressure and 65-70 mm Hg. While the parameters of the curves varied from dog to dog, the curves kept their unique shape in the individual dog for at least 1 week. C.C.O. had no effect on the plateau-level of the P.R.A.-difference (C:0.98 +/- 0.14, C.C.O:0.99 +/- 0.14 ng AI . ml-1 . h-1) and on the slope of the curve below threshold pressure (C:-0.379 +/- 0.041, C.C.O:-0.416 +/- 0.082 ng AI . ml-1 . h-1 . mm Hg-1) but shifted the stimulus-response curve to the right and increased threshold pressure (C:92.7 +/- 2.8, C.C.O:109.7 +/- 4.1 mm Hg; P less than 0.05). Renal blood flow, which was measured simultaneously in three of the dogs, showed good autoregulation down to 70 mm Hg under resting conditions and was not affected by C.C.O. except for a 30% reduction of renal blood flow at the lowest pressure step (70 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)