Anomalous replacement of foetal enterocytes in the neonatal pig.

Abstract

The fine structure of intestine from pigs 8 days old has been studied by using transmission and scanning electron microscopy of tissues fixed normally or after limited contact with distilled water. Two types of enterocyte were identified in sections of normally fixed tissue. The first, containing an apical tubular system, is considered to represent the remains of an enterocyte population already present at birth (the foetal type). The second, containing much rough endoplasmic reticulum and none of the structures listed above, is considered to represent the type of enterocyte produced postnatally (the adult type). Additional features used to distinguish these two types of enterocyte are the length of microvilli (longer for the foetal than for the adult type) and the width of the terminal web (wider for the adult than for the foetal type). Treatment of intestine from pigs 8 days old with distilled water for 30 s causes foetal-type enterocytes to swell preferentially. Their position on the villus can then be identified by using scanning electron microscopy. Foetal-type enterocytes are largely, but not entirely, confined to the upper regions of individual villi. A small proportion of foetal-type enterocytes exist in the mid villus region, either singly or in patches entirely sur­rounded by adult-type enterocytes. These results are taken to provide direct evidence for the irregular replacement of foetal-type by adult-type enterocytes in the immediate postnatal period of development. The possible effect that this might have on the susceptibility of neonatal pigs to enteric disease is discussed.