Cytoplasmic Bodies Containing Mitochondria, Ribosomes, and Rough Surfaced Endoplasmic Membranes in the Epithelium of the Small Intestine of Newborn Rats

During recent years cytoplasmic corpuscles commonly known as dense bodies, lysosomes, multivesicular bodies, cytosomes, phagosomes, and microbodies have attracted much attention (see reviews by de Duve (3) and Novikoff (5)). Probably the different terms cover the same concept in several cases, but it is not clear what the exact relationship between these various corpuscles is, and whether they bear a possible relationship to other cell components. During a study of the epithelium of the small intestine in newborn rats we found in several instances cytoplasmic bodies containing mito-chondria, vesicles, ribosomes, and rough surfaced endoplasmic reticulum. Mitochondria and what looks like mitochondrial residue have been observed earlier in cytoplasmic bodies in the epi-thelium of the small intestine of adult mice (11). In the proximal tubule cells of the kidney of infant mice, Clark (2) found membrane-bounded cytoplasmic bodies and vacuoles which sometimes contained lamellar inclusions and altered mito-chondria. Similar cytoplasmic vacuoles containing mitochondria in apparently varying states of disintegration have been observed by Novikoff (4) in the proximal tubule cells in experimentally produced hydronephrosis. As far as we know, bodies with incorporated rough surfaced endoplasmic reticulum have not been reported. MATERIAL AND METHOD The upper portion of the small intestine of newborn rats was used for this investigation. The animals wcre withdrawn from their mother immediately after birth and were examined non-fed. The tissue was removed under light ether anesthesia and fixed in cold, buffered osmium tetroxide (Paladc (6)) following the procedure given by SjSstrand (9). Embedding was done in Vestopal (8). Sections were stained with 4 per cent uranyl acetate solution (10) for 1 or 2 hours and studied in a Philips electron microscope, type EM 100 B. OBSERVATIONS AND COMMENTS Fig. 1 shows a cytoplasmic body from the basal part of an epithelial cell from a crypt anlage. In the lower part of the body a mitochondrion is seen containing three osmiophilic bodies. Above this is an area with free ribosomes and two ribosome-covered membranes separated by a space, as in endoplasmic reticulum. The upper part of the body consists mainly of wrinkled membranes in a rather dense substance. Fig. 2 shows another section through the same body. The rough surfaced membranes can here be followed for a longer distance. With the possible exception of the upper part, the cytoplasmic body is limited by a membrane FIGURE 1 Electron micrograph of the basal portion of an epithelial cell from …