Renal and tubuloglomerular feedback responses to plasma expansion in the rat

Abstract

The hemodynamic and single nephron responses of rats were studied before and after infusion of 2.5% body weight of littermate plasma given over 20 min (PVE). Renal blood flow (RBF) and kidney glomerular filtration rate (GFR) both increased approximately 40% after PVE. Blood pressure increased slightly and urine flow rate and Na+ excretion increased severalfold. Plasma colloid osmotic pressure increased from 12.7 .+-. 0.5 to 16.3 .+-. 0.9 mmHg (means .+-. SE); arterial hematocrit decreased. Single nephron GFR (SNGFR) measured at distal tubule sites increased from 22.8 .+-. 2.4 to 27.3 .+-. 1.6 nl/min. A significant differnece between paired SNGFR measurements from proximal and distal tubule sites was observed in the control period (6.7 .+-. 0.7 nl/min) and was not altered by PVE, although distal volume delivery was increased 2-fold. Tubuloglomerular feedback activity, assessed by changes in proximal tubule stop-flow pressure in response to changes in late proximal microperfusion rate, was significantly reduced after PVE. Tubuloglomerular feedback responsiveness to a given distal volume delivery was decreased and may be responsible for the increased RBF and GFR observed after PVE.