Resetting of pressure-dependent renin release by intrarenal α1-adrenoceptors in conscious dogs

We investigated the influence of a stimulation of intrarenal -adrenoceptors on the relationship between renin release and renal artery pressure in 8 conscious, chronically instrumented dogs receiving a normal salt diet. Renin stimulus-response curves were determined by a stepwise reduction of renal artery pressure down to 70 mm Hg (1) under control conditions, (2) during a bilateral common carotid occlusion combined with an intrarenal prazosin infusion, and (3) during an intrarenal methoxamine infusion. Both drug infusions did not alter resting renal blood flow. (1) The control renin stimulus-response curve revealed a flat portion (platcau-level) around and above the resting blood pressure and a very steep portion (slope) below a well-defined threshold pressure 10–15 mm Hg below the resting blood pressure. (2) An intrarenal -adrenoceptors blockade by prazosin prevented the resetting of the threshold pressure which is regularly observed during bilateral common carotid occlusion. (3) An intrarenal infusion of the -adrenoceptors agonist methoxamine increased the threshold pressure. We suggest that the neural control of renin release within the autoregulatory range of renal blood flow involves two independent mechanisms: the direct release of renin from juxtaglomerular granular cells by -adrenoceptors, and the modulation of the threshold pressure of pressure-dependent renin release by intrarenal -adrenoceptors. The small changes in renal nerve activity necessary to reset the threshold pressure and the close relationship between the threshold pressure and resting blood pressure imply an important function of intrarenal -adrenoceptors in the regulation of renin release. Our results explain controversial observations regarding the role of intrarenal -adrenoceptors in the control of renin release.This study was supported by the German Research Foundation (FG Niere, Kr. 546/5-1, Projekt 4)