Resetting of pressure-dependent renin release by intrarenal alpha 1-adrenoceptors in conscious dogs.

We investigated the influence of a stimulation of intrarenal alpha 1-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 (plateau-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 alpha 1-adrenoceptor 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 alpha 1-adrenoceptor 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 beta 1-adrenoceptors, and the modulation of the threshold pressure of pressure-dependent renin release by intrarenal alpha 1-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 alpha 1-adrenoceptors in the regulation of renin release.(ABSTRACT TRUNCATED AT 250 WORDS)