Superficial and Juxtamedullary Nephron Function during Saline Loading in the Dog

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Abstract

A modification of the microdissection technique of Hanssen was utilized in dogs to measure superficial (SNGFR) and juxtamedullary nephron filtration rate (JMGFR) in control and saline-expanded dogs. During control studies SNGFR was 60±4 and JMGFR was 72±5 nl/min. During saline loading SNGFR was 74±8 and JMGFR was 65±6 nl/min. The ratio SNGFR: JMGFR significantly increased from 0.84±0.03 to 1.15±0.08. Glomerular perfusion rate (GPR) was measured with the microsphere method during control and saline loading. Superficial GPR did not change significantly but juxtamedullary GPR increased from 225±42 to 323±39 nl/min. Calculated superficial nephron filtration fraction was unchanged after saline expansion but juxtamedullary filtration fraction decreased from 0.34±0.07 to 0.24±0.07. The data demonstrate a tendency for filtration to shift toward the superficial part and plasma flow toward the deep part of the kidney cortex. GFR in juxtamedullary nephrons appears to be less plasma flow-dependent than in superficial nephrons. The fall in filtration fraction in the deep cortex may affect sodium excretion by juxtamedullary nephrons.

Authors

Frank J. Bruns, Edward A. Alexander, Arthur L. Riley, Norman G. Levinsky