Glomerular filtration rate and effective renal plasma flow following treatment with phenobarbital

SPF-male rats were treated intraperitoneally with phenobarbital (30 mg/kg/day) or 0.9% sodium chloride for 4 days. Endogenous creatinine clearance in conscious rats and inulin clearance in nondiuretic rats under inactin anesthesia were measured 24 hr following the last injection. In an additional group of treated rats diuresis was induced by sodium chloride and mannitol and then inulin- and PAH clearance were measured simultaneously. Following 4 days treatment with phenobarbital, endogenous creatinine clearance and inulin clearance were not significantly different in control and phenobarbital-treated animals. In contrast significant changes were found in urine volume and PAH clearance in the phenobarbital-treated animals. These results do not reflect any change in glomerular filtration rate, but might be attributed to an increase in renal plasma flow or an activated tubular transport system following phenobarbital administration.