Endocrine cells in the caecum of the rabbit.

An ultrastructural study of the caecal mucosa of the rabbit revealed four endocrine cell types, distinguishable by their morphological features and by the size and appearance of the secretory granules which they contained. Endocrine cells occurred most frequently in the mid-region of the corpus ceci, with fewer cells in other regions of the caecum. The commonest cell type appeared to belong to the widely distributed enterochromaffin cells of the intestinal mucosa; less common were cells corresponding to the L cells of the colon, and more rare were endocrine cell types which corresponded to the M and (probably) S cells of the gastrointestinal tract. The secretions from these cell types may well be important in the diurnal physiological regimen of the rabbit caecum.