Endocrine cells do not exist in rat Brunner's glands. An electron microscopic study

It was revealed by light microscopic experiments that in Brunner's glands and the epithelium of the human and mammalian duodenum, cells were present, with basally lying granulations. These granules could be identified at the ultrastructural level as accumulations of pleomorphe electron-dense granules ('argentaffin', 'chromaffin' and 'osmiophilic' granules). Depending on the light and electron microscopic staining techniques used, these cells were classified as 'mucous', 'serous', or 'endocrine' ('enteroendocrine', 'paracrine' and 'enterochromaffin') cells. In the present study, the following ultrastructural morphological criteria of Brunner's gland cells were correlated: size, shape and electron density of their nuclei and nucleoli with morphological changes of their cytoplasmic and intranuclear organelles, which serve the synthesis of mucopeptides. This proved that the synthesis of mucopeptides occurred in 3 phases. The first phase served the intranuclear synthesis of organelles, which latterly were used for the cytoplasmic mucopeptide synthesis. This phase was characterized by the appearance of an electron-lucent and euchromatic nucleus, which also contained an euchromatic and electron-lucent nucleolus, and a thin electron-dense nucleus membrane (euchromatic phase). Only a few freely lying ribosomes, membrane-bound ribosomes (rough endoplasmic reticulum, RER) and mitochondria were dispersed throughout the cytoplasm. Therefore, the cytoplasm appeared electron-lucent and nearly empty. The second phase was characterized by a round but heterochromatical nucleus containing also a heterochromatic nucleolus, and the appearance of receptosome- (endosome, endocytotic vesicle) and lysosome-like structures near to the cytoplasmic membrane of the basal cell portion, as well as in the basal and lateral perinuclear region (early heterochromatic phase). The receptosome-like structures were round-oval and contained a single electron-lucent inclusion vesicle, which had an empty space or an electron-opaque granule. Both inclusion structures were located eccentrically on the inner surface of the membrane of the receptosome-like structure. Here and there, it was possible to visualize great receptosome-like structures (multivesicular bodies) containing numerous membranous electron-lucent and electron-opaque inclusion vesicles. Electron-dense pleomorphe lysosome-like structures, bearing 1-4 electron-lucent inclusion vesicles with faint grains in their spaces, were also recognized in the basal cell portion, as well as in the basal and lateral perinuclear region.(ABSTRACT TRUNCATED AT 400 WORDS)