Effect of reduced perfusion pressure on intrarenal distribution of blood flow in dogs.

Abstract

AbstractExperiments by Barton et al. (1968) and Hollenberg et al. (1968) suggested that renal sodium excretion may be regulated by the distribution of blood flow within the kidney. Such a mechanism might account for the reduction in sodium excretion during lowering of arterial perfusion pressure, despite constant glomerular filtration rate and total renal blood flow (RBF). In the present study, renal blood flow in the outer half of the cortex (OCF) and inner half of the cortex (ICF), and in outer medulla (MBF), was examined during reductions of mean renal arterial pressure (RAP). RAP was reduced in steps by a clamp on the aorta or the renal artery, and at each pressure reduction OCF and ICF (cortex group, 7 dogs) and MBF (medulla group, 11 dogs) were measured by polarographic recording of hydrogen gas clearance with platinum electrodes inserted in the cortex, 2–3 mm and 6–7 mm respectively, and in outer medulla. RBF was measured by an electromagnetic flowmeter. At control pressure, OCF averaged 3.26 ml/min · g and ICF 3.45 ml/min · g, the difference between them being insignificant. An average decrease in RAP from 131 mm Hg to 76 mm Hg caused a 1% decrease in RBF and decreases in OCF and ICF to 89% (range 77–98%) and 87% (range 75–94%) respectively, both in per cent of control. The difference between OCF and ICF during clamping was not significant. At an average decrease in RAP from control of 126 mm Hg to 88 mm Hg, RBF decreased to 96% of control; MBF was not reduced (range 81–116%). The difference between changes in MBF and RBF was not significant. Atropinization did not change the pressure‐flow relationship of outer medulla.