Effect of sympathetic stimulation and intrarenal alpha-blockade on the secretion of renin by the human kidney.

This study was initiated to explore the possible involvement of renal alpha-adrenoceptors in the regulation of active and inactive renin. In fifteen hypertensive patients who proved not to have vascular abnormalities on diagnostic renal arteriography, blood samples were collected simultaneously from the renal artery and vein before and during an intrarenal infusion of either saline (n = 5), or the alpha-1 blocker doxazosin (n = 5) or the non-selective alpha-1 blocker doxazosin (n = 5) or the non-selective alpha-blocker phentolamine (n = 5). Subsequently, responses of renal blood flow and renin secretion were assessed following 3 min of handgrip exercise. In none of the experiments secretion of inactive renin could be detected. Release of active renin increased from 580 (SEM 170) to 650 (SEM 220) microU min-1 (100 g)-1 during infusion of doxazosin (P less than 0.05) and from 760 (SEM 100) to 1000 (SEM 340) microU min-1 (100 g)-1 during infusion of phentolamine (P less than 0.01). Saline infusion had no effect on secretion of active renin. While handgrip exercise had no significant effect on active renin secretion in the saline and in the doxazosin group, it enhanced secretion from 1000 (SEM 340) to 1280 (SEM 390) microU min-1 (100 g)-1 in the phentolamine group (P less than 0.01). The results indicate that mainly alpha-2 adrenoceptors exert an inhibitory effect on release of active renin, although alpha-1 receptors participate to some degree. There is no evidence that the kidney secretes inactive renin.