Detection of endocrine cells by immunofluorescence method in the gastroenteropancreatic system of the adult eel, glass-eel, and leptocephalic larva (Anguilla anguilla L.).

Five antisera against insulin (Ins), glucagon (Glu), somatostatin (SRIF), met-enkephalin (met-enk), and serotonin (5-HT) were used for immunofluorescence detection of endocrine cells in pancreas and gastrointestinal tract (GIT) of the European eel (Anguilla anguilla L.) at three stages of development (leptocephalic larva, glass-eel, and adult eel). Comparable distribution of endocrine cells was observed for adults and glass-eels. In their pancreatic islets, positive immunoreactions were obtained only for Ins, SRIF, and Glu; this later was also present in the pancreatic ducts. 5-HT cells were present throughout the GIT. SRIF cells were situated mostly in the stomach and less in the intestine. Met-enk cells were abundant in the pyloric cecum, but less frequent in the intestinal mucosa. Glu cells were present only in the intestine. No insulin-immunoreactive cells could be detected in the GIT. The pancreatic islets of leptocephalic larvae exhibited a strong reaction for SRIF, a weak reaction for Glu, and none at all for Ins, met-Enk, or 5-HT. The GIT of these larvae contained numerous met-enk cells, mainly in the foregut. In the fore- and midgut, cells exhibited a weak fluorescence after treatment with Glu antiserum. No positive immunoreactive cells were observed with 5-HT, SRIF, or Ins antisera.