The differentiation of entero-endocrine cells of pre- and postnatal rats: light and electron microscopy and immunocytochemistry.

The differentiation of cholecystokinin/gastrin (CCK/GA)-, glucagon (GLU)- and somatostatin (SOM)-positive cells in the pre- and postnatal rat duodenum was investigated with a special emphasis on the relationship to that of the fibromuscular intestinal wall by light and electron microscopy and immunocytochemistry. Between prenatal days 16 and 21, contacts of mesenchymal cells with the epithelium are frequent, and the differentiation of the entero-endocrine cells which occasionally display a secretory function becomes advanced in close proximity to an extensive capillary network in the underlying connective tissue. CCK/GA-positive cells can be detected by immunocytochemistry in the intestinal epithelium at prenatal day 18. Other types of entero-endocrine cells are not detected until prenatal day 19. Quantitative analysis demonstrates that the volume density of CCK/GA-positive cells per 100 microns2 cytoplasmic area increases sharply at postnatal day 5 relative to earlier stages. This may be mainly due to suckling of the neonatal rat.