Differing potencies of muscle relaxants on rat and guinea-pig phrenic nerve diaphragm preparations

The sensitivities of two in-vitro preparations to neuromuscular blocking agents have been compared. The guinea-pig phrenic nerve diaphragm preparation proved to be more sensitive to vecuronium, atracurium and pancuronium than the equivalent preparation from the rat. Only tubocurarine had a similar potency on the preparations from both species. This would suggest that the guinea-pig diaphragm would be the most appropriate bioassay preparation if only small quantities of drug were available. Small differences in the cholinesterase content of the preparations was not thought to be a likely reason for the differences between the two preparations.