AN IMMUNOHISTOCHEMICAL AND MORPHOMETRIC ANALYSIS OF INSULIN, INSULIN-LIKE-GROWTH-FACTOR-I, GLUCAGON, SOMATOSTATIN, AND PP IN THE DEVELOPMENT OF THE GASTROENTEROPANCREATIC SYSTEM OF XENOPUS-LAEVIS

The ontogeny of the classical islet hormones insulin (INS), glucagon ( GLUC), somatostatin (SOM), and pancreatic polypeptide (PP) as well as insulin-like growth factor I (IGF-I) in the gastro-entero-pancreatic ( GEP) system of Xenopus laevis (stages 41-66) was studied using double immunofluorescence and morphometric analysis. As early as stage 41, cl ustered INS-immunoreactive (-IR) and isolated GLUC-IR cells occurred i n the pancreas. The first SOM-IR cells appeared at stage 43, followed by PP-IR cells at stage 46. About 79% of the PP immunoreactivity was c onfined to a subpopulation of the GLUC-IR cells. Both the GLUC/PP-IR c ells and the PP-IR cells were located in a distinct area of the pancre as. The first islets occurred in premetamorphosis (around stage SO) an d comprised mainly INS-IR and GLUC-IR cells. The majority of SOM-IR, P P-IR, and GLUC/PP-IR cells was dispersed. The numbers of hormone cells remained quite constant until the end of prometamorphosis (stage 58). Around stages 60-62, the islets were partly disintegrated and the num bers of islet cells slightly decreased. At stage 63, the cell number b egan to increase and reached the levels typical for the adult around s tage 66. After metamorphic climax, the islets were reformed. In the ga strointestinal tract, transient INS-IR cells occurred prior to the ada ptation of the gastrointestinal tract to feeding (stages 41-44) and du ring metamorphosis when there is remodeling of the gastrointestinal tr act (stages 60-63). Therefore, INS released from the transient mucosal INS-IR cells may be involved in the temporary proliferation of mucosa l epithelial cells. The first GLUC-IR and SOM-IR cells were seen at st age 41.. PP-IR cells followed at stage 46. In contrast to the islets, GLUC-IR and PP-IR cells constituted different cell populations. Around stage 46, the first IGF-I immunoreactions appeared in the GEP-system In pancreas, IGF-I immunoreactivity was found in the GLUC/PP-IR cells (85-99%) but was absent from INS-IR, GLUC-IR, and SOM-IR cells. The IG F-I-IR gastro-entero-endocrine cells, however, seemed to contain none of the classical islet hormones. (C) 1998 Academic Press.