Extraction techniques for gastrins and cholecystokinins in the rat central nervous system

Samples of rat striatum and synthetic sulphated cholecystokinin octapeptide were extracted by different procedures and the solubilised cholecystokinin-like immunoreactivity analysed by gel filtration and ion-exchange chromatography. Ice-cold 90% methanol extraction gave the greatest recovery of tissue immunoreactivity without any major modification of the extracted components. The 33-amino acid form of cholecystokinin was poorly recovered by this extractant . Boiling water or a combined boiling water/acetic acid extraction gave efficient recovery of tissue immunoreactivity but chemically modified a substantial part of the octapeptide-like component. Boiling in acetic acid alone also produced this modification but in addition resulted in poor recovery of the octapeptide-like component. The combined water/acetic acid extraction gave reasonable to good recovery of all added cholecystokinins and gastrins, including the 33-amino acid form of cholecystokinin. Ice-cold 0.1 M HCl was less efficient than 90% methanol at solubilising tissue immunoreactivity and resulted in a substantial modification of the octapeptide component distinct from that produced by boiling extractions, possibly desulphation . The results show that more than one extraction procedure is needed to study all the cholecystokinin components in brain tissue and demonstrates the necessity of using at least two chromatographic systems for such studies.