Response of the avian kidney to acute changes in arterial perfusion pressure and portal blood supply

Domestic fowl kidneys autoregulate total renal blood flow and glomerular filtration rate (GFR) over a wide range of renal arterial perfusion pressure (RAPP). Sustained (approximately 2-4 h) restriction of renal portal blood flow attenuates the autoregulatory responses. The present study was designed to assess the effects of acute (approximately 10 min) alterations of renal portal blood flow on renal function, and to dissociate the renal responses to altered renal portal blood flow from the renal responses to reductions in RAPP. The thermal pulse decay (TPD) technique and p-aminohippuric acid clearance (CPAH) were used to measure blood flow. During acute increases and decreases in renal portal blood flow, regional renal blood flow as measured by the TPD system (RBFTPD) was significantly positively correlated with total kidney blood flow represented by CPAH (RBFPAH). These results indicate that changes in total kidney blood flow induced by alteration of portal perfusion were reflected in the regional measurement of renal blood flow. Changes in renal portal blood flow did not affect the urine flow rate (UFR), GFR, or fractional excretion of sodium (FENa). Reducing RAPP from 120 to 50 mmHg significantly reduced UFR, GFR, and FENa. Overall, these results indicate that large acute changes in renal portal blood flow can significantly alter total renal blood flow without significantly affecting parameters (UFR, GFR, and FENa) primarily influenced by the renal arterial vasculature.