Co-localisation of substance P-, bombesin- and peptide histidine isoleucine (PHI)-like peptides in gut endocrine cells of the dogfish Scyliorhinus stellaris.

The gastrointestinal tract of cartilaginous fishes, like that of higher vertebrates, is known to contain endocrine cells and nerves immunoreactive for a wide variety of peptides, some of which have been structurally characterised. Since we have found that substance P-, bombesin- and peptide histidine isoleucine-like immunoreactivities are similarly distributed in the endocrine cells of the dogfish pyloric stomach, we have tried to establish whether any of these peptides are co-localised. The cells were compared in thin serial sections with both light- and electron microscopical immunocytochemistry. Double immunolabelling was also used to show two immunoreactive peptides in the same tissue section. Further characterisation of the immunoreactivity was attempted by preabsorbing the antibodies with various peptides or synthetic fragments of peptide molecules. Immunoreactivity for all three peptides was frequently present in the same cells, whereas antibodies to other peptides such as gastrin and somatostatin marked different cells. Electron microscopy indicated that all the secretory granules in three morphologically different cell types reacted with antibodies to all three peptides. Dual localisation of unrelated peptides in endocrine cells or nerves is established in many cases, but triple localisation is as yet unusual. The immunoreaction for bombesin-like peptides is different in endocrine cells and nerves, indicating that dogfish bombesin may be present in two forms, in agreement with biochemical evidence.