Inability of Parallel Bio-assay to recognize Acetylcholine in Mixtures of Substances with Acetylcholine-like Activity

Abstract

IN 1929, Dale and Dudley¹ described the parallel bioassay technique. Using three test preparations, these authors found that with acetylcholine as reference standard, the material extractable from ox spleen assayed identically in each instance. These results greatly supported other evidence obtained in that investigation and enabled them to conclude that the active material was acetylcholine. However, twenty-four years later, Banister et al.² showed that, in addition to acetylcholine, ox spleen extracts contained propionyl choline and other unidentifiable material which had acetylcholine-like activity. Clearly the parallel bioassay did not differentiate between the components of the mixture of active compounds present in the extract. In 1933, Chang and Gaddum³ showed that acetylcholine could be distinguished from pure samples of other choline esters on several biological test preparations. Recently, Hosein and his associates^4,5 have shown that, on the basis of micro-chemical analysis, the material with acetylcholine-like activity extractable from rat brain was a mixture of at least three choline esters and of four betaine CoA esters. Because of the reliance on the method of parallel bioassay to identify acetylcholine in extracts and tissue preparations^6–8, it was decided to determine whether this method could actually identify acetylcholine in mixtures of substances, all of which possessed acetylcholine-like activity.