The thrombolytic efficacy of recombinant unglycosylated full length single chain urokinase-type plasminogen activator (rscu-PA, saruplase), applied either as single intravenous bolus or as a continuous infusion over 60 minutes, was studied in 5 randomized blinded groups of 5 dogs with combined copper coil induced coronary artery thrombosis and 125I- fibrin labeled femoral vein clots. Infusion of 1 mg/kg recu-PA (group I) induced coronary recanalization in 4 of 5 dogs and 98 +/- 1% (mean +/- SEM) venous clot lysis. Bolus injection of 1 mg/kg recu-PA (group II) caused reflow in 3 of 5 dogs and 88 +/- 5 percent venous clot lysis. Infusion of 0.5 mg/kg rescu-PA (group III) achieved reflow in 3 of 5 dogs and 52 +/- 6% venous clot lysis. Bolus injection of 0.5 mg/kg rscu-PA (group IV) induced reflow in 4 of 5 dogs and 48 +/- 12% venous clot lysis. Placebo infusion (group V) was associated with late recanalization in 1 of 5 dogs and 18 +/- 8% venous clot lysis. Coronary artery reocclusion after reflow was not observed in groups I and II, but occurred in 2 of 3 animals in group III and in 3 of 4 animals in group IV (P = .02). The time to reflow in responsive animals was 22 +/- 5 minutes with infusion of 0.5 or 1 mg/kg rscu-PA and 14 +/- 1 minute with bolus injection of 0.5 or 1 mg/kg (P = .14). Depletion of fibrinogen and alpha 2-antiplasmin to less than 25% of baseline levels was observed in the 5 dogs given 1 mg/kg rscu-PA by bolus and in 3 of the 5 dogs given 1 mg/kg rscu-PA via infusion, but in none of the dogs that received 0.5 mg/kg rscu-PA (P less than .001). Plasma clearance rates were 170 +/- 44 and 230 +/- 30 mL/minute after bolus injection and 190 +/- 47 and 310 +/- 56 mL/minute during infusion of rscu-PA for the 1 mg/kg and 0.5 mg/kg doses respectively. Thus, intravenous bolus injection of rscu-PA (saruplase) appears to be equipotent to an infusion over 60 minutes for both coronary and venous thrombolysis. This animal model of combined arterial and venous thrombolysis may be useful for the evaluation of new thrombolytic strategies.