Evidence for altered glomerular hemodynamics during acute nephron obstruction.

The stop-flow technique has been used to estimate mean glomerular capillary hydraulic pressure (PGC). This technique involves complete obstruction of fluid flow in single proximal tubules, thereby altering the formation of glomerular filtrate as well as the delivery of fluid to more distal segments of the same nephron. To determine whether tubule obstruction affects PGC, pressures were measured in capillaries of accessible glomeruli before and during proximal tubule obstruction in hydropenic Munich-Wistar rats. The results were compared with estimates of PGC obtained for these same glomeruli by the stop-flow technique. When glomerular filtration was unhindered, blockade of fluid flow into the loop of Henle did not alter directly measured PGC values. When glomerular filtration was stopped by proximal tubule obstruction, directly measured PGC values increased by approximately 7 mmHg. Stopping glomerular filtration also increased postglomerular capillary hydraulic pressure, suggesting that acute single nephron obstruction and cessation of filtration substantially affects these pressures by diverting fluid to the postglomerular capillary bed. Indirect stop-flow estimates of PGC did not differ from direct measurements of PGC in the same glomeruli during stopped flow. Thus, in the normal hydropenic condition, stop-flow estimates of PGC accurately measure PGC. However, the PGC value prevailing under the stop-flow condition is substantially elevated over the PGC existing when filtration is proceeding normally.