Immunocytochemical investigation of the gastro-entero-pancreatic (GEP) neurohormonal peptides in the pancreas and gastrointestinal tract of the dogfish Squalus acanthias.

The pancreas and gastrointestinal tract (GIT) of adults and of an embryonic stage of 11 cm long (about half the length of newborn fish) of the spiny dogfish, Squalus acanthias, were investigated immunocytochemically for the occurrence of the gastro-entero-pancreatic (GEP) neurohormonal peptides. In the pancreas of adult forms 5 endocrine cell types were seen, namely insulin-, somatostatin-, glucagon-, pancreatic polypeptide (PP)- and gastric inhibitory peptide (GIP)-immunoreactive cells. These cell types form scattered islets and were seen sometimes to surround small ducts. GIP-immunoreactivity cells did not occur in glucagon-containing cells. In the mucosa of GIT of adults 18 endocrine cell types were observed, viz. insulin-, somatostatin-, glucagon-, glicentin, PP-, polypeptide YY (PYY)-, vasoactive intestinal polypeptide (VIP)-, GIP-, gastrin C-terminus, CCK-, neurotensin N-terminus-, bombesin/gastrin releasing peptide (GRP)-, substance P-, enkephalin-, alpha-endorphin, beta-endorphin-, serotonin- and calcitonin immunoreactive cells. These cells occurred mostly in the intestine. All these cell types were of the open type, except glucagon- and glicentin-immunoreactive cells in the stomach, which seemed to be of the closed type. In the muscle layers and the submucosa, VIP and substance P- immunoreactive nerves and neurons were observed. In the pancreas of the dogfish embryo only 3 endocrine cell types could be demonstrated, namely insulin-, somatostatin- and glucagon-immunoreactive cells. In the mucosa of the GIT of the embryos studied 12 endocrine cell types were detected, viz. insulin-, somatostatin-, glucagon-, PP-, PYY-, VIP, GIP, gastrin C-terminus-, CCK-, neurotensin N-terminus-, enkephalin- and serotonin immunoreactive cells. The number of these cells, except that of PYY-immunoreactive cells, was lower than that of adults and in some cases their distribution did not correspond with that of adults.