ULTRASTRUCTURAL CLASSIFICATION OF THE ENDOCRINE-CELLS OF THE LARGE-INTESTINE OF THE CALF - CYTOCHEMICAL EVIDENCE OF THE PRESENCE OF VIALLISS PRE-EC CELLS

GEP (Gastro-Entero-Pancreatic) endocrine cells were very numerous in t he mucosal layer of the large intestine of the calf. Their frequence a ppeared to increase towards the distal portions of the gut. Endocrine cells were dispersed among epithelial cells lining intestinal glands a nd were frequently grouped together. Cellular shape was pyramidal or e longated; the cytoplasm was electron-lucent and contained highly chara cteristic secretory granules. Six different types of endocrine cells w ere identified on the basis of the ultrastructural aspect and cytochem ical characteristics (silver-reactivity) of their secretory granules: EC, L, PP, A, D-1 and D cells. EC and L cells were the most abundant i n all localisations. They were especially numerous in the rectum. A su bpopulation of EC cells was negative to Masson-Singh's reaction showin g that they lack 5-HT. This observation enabled us to refer this latte r cellular type to the ''pre-EC'' cells, described by Vialli as an ear lier evolutive step of the EC cells population. Their presence in the calf gut might be linked to its possible ''immaturity'', due either to the age or to the alimentary diet.