Baroreflex sympathetic activation increases threshold pressure for the pressure-dependent renin release in conscious dogs
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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 inique 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 Al·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 Al·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<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).
β-Adrenergic blockade in 4 of the dogs reduced the plateau-level of the P.R.A.-difference from 0.86±0.19 to 0.36±0.05 ng AI·ml−1·h−1 (P<0.05) but had no effect on the increase of threshold pressure elicited by C.C.O.
It is concluded that the stimulus-response curve for the pressure-dependent renin release has a remarkable long-term stability in the individual dog. The curve is shifted to the right by a moderate carotid baroreflex increase of renal sympathetic nerve discharge which leaves total renal blood flow largely unchanged. It is suggested that the increase in threshold pressure is independent of β-adrenergic effects.
Key wordsBlood pressure Kidney blood flow Autoregulation Renin release Pressoreceptors
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