Substance P in the argentaffin carcinoid of the caecum: biochemical and biological characterization.

An argentaffin carcinoid tumour of the caecum which contained serotonin (167 micrograms/g) and consisted predominantly of EC1-cells, was analysed for the presence of peptides using immunohistochemical, biochemical and pharmacological methods. A very high content of 3.9 micrograms/g of immunoreactive substance P was found. The distribution of cells staining positively for substance P matched that of cells containing serotonin. While some immunoreactive somatostatin (3.2 ng/g) was present in the tumour, neurotensin, glucagon, gastrin, and motilin were not found. Part of the substance P immunoreactivity measured most likely represents authentic substance P: it behaved like substance P in two chromatographic systems and in two bioassays, and its activity on the guinea pig ileum was abolished by specific tachyphylaxis towards substance P.