Dynamics of renal excretion of phenol and major metabolites in the rainbow trout (Oncorhynchus mykiss)

Renal excretion of phenol (PH), phenyl glucuronide (PG), phenyl sulfate (PS), and hydroquinone (HQ) was determined in 600-900 g rainbow trout (Oncorhynchus mykiss) continuously exposed (144-h) to waterborne PH (5 mg l-1 or 53.2 μmol l-1) in respirometer-metabolism chambers. The 'free' plasma concentration time course was obtained from samples withdrawn from a dorsal aortic cannulae, while the urine concentration time course was acquired using a bladder catheter. Microdialysis and HPLC techniques were used to isolate and identify PH and metabolites. Plasma and urinary PH were at steady-state in 4 h. PG and HQ in both plasma and urine continued to rise throughout 144 h. PS values in plasma reached a maximum around 48 h. while urine PS plateaued near 24 h. Of the net PH gill uptake at steady-state (144 h), as much as 50% was eliminated in the urine (PG = 81. PS = 16, PH = 4%) and the rest extrarenally. PS kinetics suggested the existence of a high affinity/low capacity pathway, while PG production was suggestive of a low affinity/high capacity formation pathway. Rainbow trout glomerular filtration rate (GFR) was 6.10 ml kg-1 h-1, which was 30% higher than the mean urine flow rate (UFR) of 4.28 ml kg-1 h 1. Renal Clearance (Clx) calculated for PH, PG, PS and HQ were 4.12, 8.67. 24.33 and 1.85 ml kg-1 h-1, respectively. Urine Clearance Ratios (Clv/GFR) were 0.69, 1.56, 5.49 and 0.30 for PH. PG, PS and HQ, respectively. The results of this stud y support in vivo tubular secretion in freshwater adapted trout for both PG and PS, and suggest a possible kidney secretory transport maxima for sulfate conjugates.