PSEUDO-CHOLINESTERASE ACTIVITY IN THE C.N.S. 251 must be stressed that these latter findings are of a preliminary nature and are as yet unsupported by any in vivo work, so that although we have evidence of an association of pseudo-cholinesterase activity with the white fibre tracts of the central nervous system we are at present unable to reach any conclusions as to its physiological function in these areas. SUMMARY 1. The relative rates of hydrolysis of a number of different choline esters by preparations from different areas of human and other mammalian brains have been determined. 2. In all the areas studied, a measurable degree of hydrolysis of benzoylcholine and butyrylcholine was observed. 3. The benzoylcholine-hydrolysing enzyme present in human nervous tisue appears to be a 'butyro-cholinesterase' closely resembling the pseudo-cholinesterase present in human plasma. 4. The white fibre tracts of the human cerebrum were found to contain significantly more of this pseudo-cholinesterase than the grey matter. Our thanks are due to the Chief Superintendent, Experimental Station, Porton, for providing us with DFP, to Dr V. P. Whittaker for a sample of propionylcholine perchlorate, and to Mr L. C. Beaney and Mr D. H. Burchett for technical assistance. We also wish to thank the Medical Research Council for a grant to one of us (M.G.O.). (Results expressed as lumoles/100 ml.) Liquid in rumen Exp. 1 Water Sodium butyrate, 0-15M Water Sodium propionate, 0-15M Water Sodium acetate, 0-15M Water Sodium butyrate, 0-15M Exp. 2 Water Sodium butyrate, 0-15M Water Sodium propionate, 0-15M Water Sodium acetate, 0-15M Water Sodium butyrate, 0-15M Rumen blood Ketone bodies Fatty acid 48 222 83 83 60 78 19 219 47 310 110 43 24 100 33 195* 334 77 118 46 369 46 611 68
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