Role of macula densa in renal nerve modulation of renin secretion.

Low-frequency renal nerve stimulation (0.25 Hz) augments the renin secretion response to reduction of renal perfusion pressure to 50 mmHg by aortic constriction. The present experiments determined whether this modulating influence could be demonstrated when the macula densa receptor was inoperative. In 10 anesthetized dogs with a nonfiltering kidney and sectioned renal nerves, aortic constriction to 52 mmHg decreased renal blood flow and increased renin secretion from 126 +/- 94 to 192 +/- 55 ng/min. During low-frequency renal nerve stimulation and aortic constriction to 50 mmHg, renin secretion was not augmented (37 +/- 13 to 81 +/- 42 ng/min). In four anesthetized dogs with nonfiltering kidneys, aortic constriction to 52 mmHg increased renin secretion similarly before (16 +/- 8 to 68 +/- 17 ng/min) and after renal denervation (14 +/- 14 to 78 +/- 18 ng/min). Therefore, the augmentation of the renin secretion response to aortic constriction to 50 mmHg by low-frequency renal nerve stimulation in filtering kidneys does not result from an interaction with the renal vascular baroreceptor or the juxtaglomerular granular cells. Since neural augmentation of renin secretion during aortic constriction was not observed in the nonfiltering kidney where the macula densa is inoperative, we conclude that the macula densa is the probable site for the neural modulation of renin secretion.