Glomerular permselectivity to serum proteins in rainbow trout (Salmo gairdneri)

Changes in glomerular filtration rate (GFR) were induced in the unanesthetized rainbow trout by short-term adaptation from freshwater (FW) to brackish water (BW, 50% seawater) to investigate the effect of altered glomerular function on the glomerular permselectivity to endogenous serum proteins in vivo. Protein patterns of serum and urine were obtained by nondenaturing polyacrylamide gradient gel electrophoresis. In the serum, high-molecular-weight proteins dominate by 83.1 +/- 8.16%, and total serum protein concentrations were 3.25 +/- 0.32 (FW) and 3.12 +/- 0.16 g/100 ml (BW). The urinary protein concentration increased from 16.0 +/- 1.41 (FW) to 42.8 +/- 11.0 mg/100 ml (BW), whereas GFR and urine flow rate, both linearly related, decreased from 4.55 +/- 0.34 (FW) to 1.84 +/- 0.11 (BW) ml.h-1.kg-1 and from 2.31 +/- 0.19 (FW) to 0.56 +/- 0.02 (BW) ml.h-1.kg-1, respectively. The fractional clearance of protein increased exponentially at decreased GFR. This suggests increased glomerular filtration of serum proteins due to altered glomerular hemodynamics.