Crude substance P from brain contains a cholecystokinin-like peptide.

The subfractions Fa, Fb, and Fc of crude substance P (SP) preparations made from human and bovine brains were analysed for SP and the COOH-terminal octapeptide of cholecystokinin (CCK-8). The methods were specific radioimmunoassays (RIAs) for SP and CCK-8, and bioassays on isolated organs of the guinea pig: the ileum, the gallbladder and the field-stimulated vas deferens. 1. In bioassays of synthetic peptides the vas deferens reacted specifically to SP and the gallbladder to CCK-8. 2. RIAs and bioassays revealed unequivocally that most of SP-like activity was present in Fb, while Fc contained mainly CCK-8-like activity. Varying results were obtained with Fa. 3. The pharmacologically active principle of Fc is CCK-8 or a closely related peptide. Earlier results concerning the pharmacological and neurochemical properties of Fc must be ascribed to this peptide.