Glomerular dynamics in dogs at reduced renal artery pressure

Abstract

Single nephron glomerular plasma flows and pressures in the dog were reduced to values similar to those in rats to evaluate whether filtration pressure equilibrium can be obtained in the dog. Reduction of renal artery pressure from 121 .+-. 7 to 65 .+-. 2 mmHg in 7 dogs decreased single nephron filtration rate from 75 .+-. 7 to 35 .+-. 3 nl/min. Single nephron glomerular plasma flow was decreased from 263 .+-. 21 to 106 .+-. 11 nl/min. Glomerular capillary pressure, estimated from stop-flow pressures in superficial nephrons, decreased from 60 .+-. 1 to 45 .+-. 1 mmHg. The effective filtration pressure decreased from 18 .+-. 1 to 9 .+-. 1 mmHg. The filtration pressure at the efferent end of the glomerular capillaries, 12 .+-. 2 mmHg (P < 0.001), decreased to 1.6 .+-. 1 mmHg, not significantly different from 0. The ultrafiltration coefficient was 4.3 .+-. 0.4 and 4.2 .+-. 0.7 nl/min per mmHg before and after pressure reduction, respectively. Reduced arterial perfusion pressure, below the autoregulatory range, was accompanied by a marked increase in superficial efferent arteriolar resistance associated with increased single nephron filtration fraction. Whole kidney filtration fraction decreased, indicating a heterogeneous vascular response to reduced perfusion pressure. When renal perfusion pressure was reduced so that glomerular plasma flows and pressures were similar to values found in rats, filtration pressure at the efferent end of the glomerular capillaries reached equilibrium in the dog.