Isoproterenol excretion and metabolism in the isolated perfused rat kidney.

[3H]isoproterenol excretion and metabolism were studied in the isolated perfused rat kidney using a one-pass, non-recirculating perfusion system with constant infusion rates of [3H]isoproterenol. The [3H]isoproterenol (U/P) to inulin (U/P) ratio was approximately 15 indicating extensive tubular secretion. A major renal metabolite, 3-O-methylisoproterenol, appeared in the urine and renal vein perfusate and also accumulated in the renal tissue. The fractional excretion of isoproterenol decreased with time while fractional excretion of p-aminohippurate remained stable. The observed decreasing urinary clearance and percent extraction of isoproterenol with time may be due to the progressive intrarenal accumulation of 3-O-methylisoproterenol.