Changes in single nephron renin release are mediated by tubular fluid flow rate

In vivo renin release from single nephrons microperfused with artificial tubular fluid was studied in recollection experiments. Renin concentration was measured in systemic arterial plasma (A-PRC) and in either early proximal tubular fluid (TFR), or in plasma from the welling point of the efferent arteriole (SV-PRC) belonging to the microperfused nephron. Micropuncture collections were controlled to maintain the proximal intratubular pressure equal to the control free-flow pressure. Increasing the Henle loop flow rate from 12 to 18, or to 34 nl/min, was followed by a significant decrease in TFR, while reducing the flow rate from 12 to 6 nl/min caused a significant increase in TFR. Similarly, increasing the Henle loop free-flow rate by 6 to 8 nl/min depressed SV-PRC, while reducing the flow rate by fluid aspiration at 8 to 10 nl/min caused a significant increase in SV-PRC. These data indicate: that renin release, to a significant part at least, occurs into the vascular lumen of the afferent arteriole: that modest changes in early distal flow rate may control renin release from the JG-cells; and that increasing the flow rate depresses renin release, and vice versa. It is suggested that the renin system is directly involved in an additional TGF mechanism controlling postglomerular vascular resistances.