134 FACTORS AFFECTING METABOLISM in vitro 



within the phosphatidic acid fraction (Hokin and Hokin, 19556). 

 The effect was found not to be specific for phosphate, the incorpora- 

 tion of inositol-2-^H into the phosphoinositide fraction being 

 stimulated 150% by 10" ^M acetylchohne (Hokin and Hokin, 

 1958(2) though the incorporation of glycerol- l-^^C into the phos- 

 pholipids was apparently unaffected. With mitochondrial and 

 microsomal fractions of brain the incorporation of phosphate into 

 the phosphatidic acids was increased if 10"* M acetylcholine, 

 together with eserine, was included in the medium from which 

 fluoride was absent. In the presence of sodium fluoride the 

 incorporation of phosphate into the phosphatidic acids was 

 increased 8-10 times more than the incorporation in the absence 

 of fluoride, acetylcholine then having no additional effect (Hokin 

 and Hokin, 19586). It is considered that the overall response to 

 acetylcholine is really an exaggeration of the type of response 

 occurring locally in cerebral tissue when acetylcholine is released 

 during nervous transmission. The reasoning here is not readily 

 followed. The concentrations of acetylcholine used are some 

 100-1000 times greater than those existing in the brain and though 

 effects have been described at lower concentrations of 10-^-10" ^M 

 these are either extremely small or apparent only upon extrapola- 

 tion of a concentration/response curve. The specificity of the 

 response to acetylcholine is also not clear, carbamylcholine at 

 10-^-10-*M having been earlier reported to increase the incorpora- 

 tion of radioactive phosphate into cerebral phospholipids to a 

 small degree (Hokin and Hokin, 1953). At present it would seem 

 that further clarification of this interesting effect is necessary before 

 correlation with events during nervous transmission can be 

 attempted. 



References 



Abood, L. G. (1954) Amer. Jf. Physiol. 176, 247. 



Abood, L. G. (1956) 20th Intern. Physiol. Congr., Brussels. Abstracts of 



communications, p. 29. 

 Abood, L. G. and Romanchek, L. (1955) Biochevi. Jf. 60, 233. 

 Abood, L. G., Gerard, R. W. and Ochs, S. (1952) Amer. J. Physiol. 171, 



134. 

 Abood, L. G., Gerard, R. W. and Tschirgi, R. D. (1952) in Phosphorus 



Metabolism, Vol II, p. 799 (Ed. by W. D. McElroy and B. Glass), 



Johns Hopkins Press, Baltimore. 



