The effect of hemorrhagic hypotension on total and local renal blood flow in the rat.

The effect of hemorrhagic hypotension (HH) on local and total renal blood flow was studied in rats. Cortical blood flow, measured as H2 gas clearance, was determined before and during HH with a mean arterial blood pressure of 50 mm Hg. During the initial 10-15 min of bleeding renal cortical vascular resistance was unchanged, and total renal blood flow autoregulatory ability was abolished. Cortical vascular resistance thereafter increased steadily to twice the control level after 90 min of HH. At this time, retransfusion of the shed blood improved cortical blood flow due to increased arterial blood pressure, not to reduced cortical vascular resistance. In a second group, total and local renal blood flows were obtained from 125I-iodoantipyrine uptake rate after 2 h of HH with arterial blood pressure maintained at 50 mm Hg. Total renal blood flow was reduced to 20% of control with no change in blood flow distribution between outer and inner cortical or medullary zones. Both cortical blood flow and intrazonal local renal blood flow heterogeneity had increased at the end of the HH period. However, ischemic and extremely low flow sectors comprising cortex and outer medulla were observed only in 1 of the 10 kidneys studied with the 125I-iodoantipyrine technique. In only 1 of 8 animals studied with the H2 gas method were intermittent sudden changes in cortical blood flow observed during HH. Since hematocrit tended to fall during HH, these observations support the concept that local flow intermittence is predominantly associated with high hematocrit shocks.