Cyanide metabolism in the isolated, perfused, bloodless hindlimbs or liver of the rat.

Female CD1 rats weighing 250-300 g were anesthetized with ip pentobarbital, 50 mg/kg, and either the liver or the hindlimbs were surgically isolated and perfused in situ with a Krebs-Henseleit buffer, pH 7.4, at 38 degrees C, containing 40 g/liter dextran and 30 mg/liter papaverine. Perfusion pressure was continuously monitored, and in most experiments, flow was maintained at the physiological rate of 8.5 ml/min. In-line Clark-type electrodes allowed the continuous measurement of oxygen extraction. Potassium cyanide to 0.15 mM was usually added to the perfusate just prior to the start of a run. After a period of equilibration, samples of the perfusate were taken periodically for cyanide (CN) and thiocyanate (SCN) analyses. The results were used to determine CN extraction ratios or clearance and rates of SCN formation. When it was apparent that a steady state had been reached with respect to the above, sodium thiosulfate (TS) was added to the perfusate (to 0.1, 1.0, or 2.0 mM), and periodic samples were again collected after an equilibration period. In the absence of albumin, TS rapidly and significantly increased the rate of conversion of CN to SCN in both the liver and the hindlimbs. The rate of CN clearance in milliliters per minute per kilogram perfused tissue was 20-fold greater in the liver than in the hindlimbs. However, when the results from hindlimbs were extrapolated to the total body skeletal muscle mass, the rate of CN clearance by the total liver mass was only 1.5-fold greater than in total muscle mass. In the absence of TS, total muscle mass cleared CN at a rate that was 2.6-fold greater than the total liver mass, but the rates in both tissues were very much less than in the presence of TS. The extraction ratio for CN in the liver was 0.8 and the clearance was dependent on the flow rate. The extraction ratio for CN in the hindlimbs was 0.2, and the clearance was independent of the flow rate. Thus, CN clearance by the liver probably increases (within limits) with increasing portal blood flow. Evidence was obtained for the existence of a significant CN "sink," particularly in the liver, which presumably represents reversible binding to unknown tissue constituents.