THE ENDOCRINE CELLS OF THE GASTROINTESTINAL MUCOSA OF A SQUAMATE REPTILE, THE GRASS LIZARD (MABUYA QUINQUETAENIATA). A HISTOLOGICAL AND IMMUNOHISTOCHEMICAL STUDY

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Abstract
Twelve endocrine cell types were observed in the gastrointestinal mucosa of the grass lizard, M. quinquetaeniata, namely enterochromaffin cells, somatostatin, glucagon, pancreatic polypeptide (PP), secretin, gastric inhibitory peptide (GIP), gastrin, cholecystokinin (CCK), CCK mid-portion, neurotensin, bombesin and non-argentaffin motilin immunoreactive cells. Enterochromaffin cells were seen throughout the gastrointestinal tract. Somatostatin, PP and neurotensin immunoreactive cells were located in both the stomach and the small intestine. Glucagon, secretin and bombesin immunoreactive cells were observed only in the stomach and GIP and motilin immunoreactive cells only in the small intestine. Gastrin immunoreactive cells were detected in the stomach by antisera specific to both the C-terminus and the mid-portion of the mammalian gastrin molecule. The C-terminus immunoreactive cells, however, outnumbered the gastrin mid-portion immunoreactive ones. In the small intestine, CCK immunoreactive cells reacted with antisera specific for the C-terminus and the mid-portion (9-20) of the CCK molecule. In the rectum CCK cells reacted only with antiserum directed against the mid-sequence (9-20) of the CCK molecule. The lizard gastrointestinal tract contains endocrine cell types homologous to those of mammals, except substance P and vasoactive intestinal polypeptide cells. The difference in the topographic distribution of some of these cell types between the lizard and mammals may reflect a difference in the digestive process and/or in the mechanism of its control.