PLACENTAL TRANSFER OF 14C LABELLED SUCCINYLCHOLINE IN NEAR-TERM MACACA MULATTA MONKEYS

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Abstract
Placental transfer of succinylcholine as 14C succinyldicholine hydroiodide was studied in 23 near-term Macaca mulatta monkeys. Succinylcholine in doses of 2 mg and 3 mg/kg body weight and in repeated doses of 2 mg and 1.2 mg/kg was injected into the maternal circulation either intravenously or into the abdominal aorta. Plasma concentrations of succinyldicholine and its products of biotransformation in the maternal and foetal circulation and in the amniotic fluid were determined at various time intervals. Placental transmission of succinylcholine was found to be rapid and more extensive than reported previously. Peak concentrations were achieved in the foetus at 5- and 10-minute periods after administration to the mother. A concentration of 0.6 μg of succinyldicholine per ml plasma was reached. Comparing this with the minimum concentration which affects the maternal e.m.g. it is likely to have a slight effect on the foetal e.m.g. but it is unlikely to depress respiration significantly in the newborn. Succinylcholine was admin istered into the foetal circulation arid a reversed transfer to the maternal circulation was demonstrated. The maternal e.m.g. was depressed slightly. The pseudocholinesterase activity in the foetus was lower than in the mother. This would explain a slower biotransformation rate of succinyldicholine in the foetus than in the mother. The transfer of succinyldicholine from the mother to the foetus and the amniotic fluid was found to be more rapid than in the reverse direction.

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