Effect of loop of Henle flow rate on glomerular capillary pressure.

Studies were performed in male Munich-Wistar rats weighing a mean of 100 g to evaluate further the hemodynamic effects of changing loop of Henle flow rate. When late proximal flow rate was varied by microperfusion from the late proximal tubule, single nephron glomerular filtration rate (SNGFR) measured in the early proximal tubule fell from 17.2 +/- 0.86 nl min-1 at a perfusion rate of zero to 11.8 +/- 0.88 nl min-1 at a perfusion rate of 14 nl min-1. Further increases in loop flow did not further depress SNGFR. Glomerular capillary pressure (Pgc) was measured directly in superficial glomeruli while loop of Henle flow was varied. Elevating loop flow was followed by a rapid decrease in Pgc, which was reversible when flow was reduced. The mean response to maximum stimulation was a decrease in Pgc of 6.6 +/- 0.7 mm Hg, and the response was close to maximum at a perfusion rate of 14 nl min-1. Parallel changes in stop-flow pressure were observed. These findings, together with previous observations that increasing loop of Henle flow results in decreased single nephron blood flow, permit the conclusion that the dominant vascular response to elevated loop of Henle flow is constriction of the afferent arteriole.