In vitro succinylcholine hydrolysis in plasma of the African elephant (Loxodonta africana) and impala (Aepyceros melampus)

In elephants the time lapsed from i.m. injection of an overdose of the muscle relaxant succinylcholine (SuCh) until death, is significantly longer than in impala. To determine a difference in the rate of SuCh hydrolysis, once the drug enters the circulation, contributes to this phenomenon we have measured the rate of hydrolysis of SuCh in elephant and impala plasma, and by elephant erythrocytes. Rate of hydrolysis was determined by incubating SuCh in plasma or erythrocyte lysate at 37 degrees C and quantifying the choline produced. Plasma SuCh hydrolytic activity in elephant plasma (12.1+/-1.7 Ul(-1) mean+/-S.D.; n=9) was significantly higher than it was in impala plasma (6.6+/-0.6 Ul(-1); n=5), but were approximately 12 and 21 times lower, respectively, than in human plasma. Elephant erythrocyte lysate had no SuCh hydrolytic activity. Applying this data to previous studies, we can show that the ratio of SuCh absorption to SuCh hydrolysis is expected to be 1.25:1 and 1.41:1 for elephants and impala respectively. It will thus take at least 1.7 times longer for elephant to achieve a plasma SuCh concentration similar to that in impala. We conclude that a more rapid hydrolysis of SuCh in elephant plasma is one factor that contributes to the longer time to death compared to impala.