Sympathetic Modulation of the Pressure-Dependent Renin Release in Conscious Dogs

Abstract

The re1ationship between mean renal artery pressure and renal venous-arterial plasma renin activity-difference (renin stimulus- response curve;RSRC) was studied in 15 conscious dogs by a stepwise reduction of renal artery pressure down to the lower limit of renal blood flow (RBF)-autoregulation. The RSRC has a flat section above threshold and a steep slope - indicating a 100% increase of renin release per 2.5 mmHg - below a well defined threshold pressure (Pth). Pth may remain unchanged for 4 weeks. A reflex activation of the renal sympathetic nerves by common carotid occlusion increased Pth by 16.5 ± 3.2 mmHg (P < 0.0l); this effect was abolished by intrarenal alpha-blockade (prazosin) .A low dose intrarenal infusion of methoxamine, which did not change RBF, increased Pth by 8.5 ± 0.7 mmHg (P<O.00l). We conclude that in the resting conscious dog renal perfusion pressure is a powerful factor in the control of renin release. The renal sympathetic nerves modulate the pressure-dependent mechanism within the autoregulatory range of renal blood flow by an alpha-adrenergic adjustment of threshold pressure.

Key Words:

• Renin Release
• Sympathetic Nerves
• Renal Baroreceptor
• Threshold Pressure