Filtration dynamics and natriuretic response to volume expansion in humans

We used differential solute clearances and a theoretical analysis of glomerular ultrafiltration and dextran sieving to characterize the hemodynamic response of nine healthy humans to infusion of isoncotic, 5% albumin in saline or saline vehicle alone. During albumin infusion (10.2 +/- 0.2 ml.kg-1.30 min-1) plasma volume increased by 18%, but oncotic pressure rose by only 0.8 mmHg. Despite the hypervolemia, renal blood flow (RBF) declined by 140 ml/min and glomerular filtration rate (GFR) declined by 16 ml/min during the infusion. RBF increased progressively postinfusion, exceeding baseline by 135 ml/min after 4 h; GFR was restored to baseline. Although oncotic pressure declined by 2 mmHg, a similar transient decline in GFR (-13 ml/min) was associated also with infusion of saline vehicle alone (9.4 +/- 0.3 ml.kg-1.30 min-1), which increased plasma volume by 9%. Sieving coefficients of dextrans (radius 32–42 A) were lowered during and after either infusion, a phenomenon that we compute to reflect a reductio...