Estimation of substance p in mouse brain. The identification of interfering nucleotides in the extract.

Substance P has been extracted from brain by previously described methods and assayed on the guinea-pig isolated ileum. The concentrations showed a wide scatter which was not due to the bioassay or to variations in the extraction procedure. Adenosine-5'-monophosphate and adenosine-5'-triphosphate have been identified in the extracts by paper chromatography and by chemical reactions. The concentrations of these substances were sufficient to interfere with the assay of substance P, adenosine-5'-monophosphate diminishing and adenosine-5'-triphosphate increasing the contractions of the ileum due to substance P. Adenosine-5'-diphosphate was also detected in the extracts but its biological activity was insufficient to influence the estimations. The concentrations of adrenaline, noradrenaline, potassium ions, sodium chloride, 5-hydroxytryptamine, and gamma-aminobutyric acid were below the threshold concentrations for interference with the assay of substance P.