No abstract

To reveal the distribution of endothelin (ET)-containing stromal cells (mast cells and macrophages), we investigated the rat gastrointestinal tract immunohistochemically using antibodies to Big ET-1, Big ET-2, Big ET-3, and mature ETs. In all the regions of the gastrointestinal tract, immunoreactivity for all the antibodies used was found in stromal cells that were located mainly in the lamina propria (not in the submucosa). The number of these cells was largest in the small intestine and smallest in the colon. Moreover, Big ET-2, which was originally identified in the gastrointestinal tract, was also found in many stromal cells, but Big ET-3-containing cells, unexpectedly, were found in almost the same number as Big ET-2-containing cells, while Big ET-1-containing cells were few. These immunopositive stromal cells seemed to be mast cells and macrophages from their histological features. Double-immunohistochemical staining revealed that 92% of the mature ETs-positive cells were mast cells; the rest were macrophages. Furthermore, we confirmed that mature ETs coexisted with ET-A or ET-B receptors in identical cells. Hence, we presume that ETs are synthesized in and secreted from stromal cells in the rat gastrointestinal tract, that their main isotypes are not only ET-2 but also ET-3, and that ETs may act in an autocrine/paracrine fashion.

No abstract

Endothelin (ET) was originally identified as a vasoactive peptide biosynthesized in vascular endothelial cells. Because ET has also been found in the brain as a neuropeptide, it has been thought to belong to the group of brain-vascular peptide hormones. To date, type A and type B receptors for ET have been found. To elucidate the topographic distribution of type A receptor (ET-AR) in the brain, we raised a specific antibody to the C-terminal (64 amino acids) peptide of rat ET-AR and immunostained rat brain sections with this antibody. Immunoreactivity for ET-AR was detected in neuronal cell bodies and also in the many proximal and some distal parts of their fibers. Nerve cell bodies containing strong ET-AR-immunoreactivity were distributed in the lateral part of the reticular formation, the nucleus of the solitary tract and its surrounding area, the dorsal midline area and medial longitudinal fasciculus, the subependymal layer of the fourth ventricular roof, the caudolateral area of the pontine tegmentum, the locus coeruleus, the rostral pontine area of the lateral reticular formation, the retrorubral area, the substantia nigra, the ventral tegmental area, the periventricular region lateral to the rostral mesencephalic aqueduct and caudal third ventricle, the arcuate hypothalamic nucleus, the caudomedial area of the zona incerta, the periventricular hypothalamic nucleus, the parvocellular portion of the paraventricular hypothalamic nucleus, and the periglomerular region of the olfactory bulb. In addition, the Purkinje cells of the cerebellar cortex, the nerve cells in the mesencephalic trigeminal nucleus, and the magnocellular neurons of the supraoptic and paraventricular hypothalamic nuclei showed weak immunoreactivity. The distribution of highly ET-AR-immunoreactive neurons is quite similar to that ofcatecholamine neurons.

Blue-green fluorescent subependymal cells with intraventricular processes were shown by the fluorescent histochemical method to be distributed from the preoptic recess to the infundibular recess of the frog hypothalamus. Electron microscopy revealed at least two types of CSF-contacting subependymal cells, type 1 containing large dense granules (about 100-200 nm in diameter) and type 2 containing small dense core vesicles (about 60-100 nm in diameter). Subsequent to fixation in permanganate solution, the small dense core vesicles in type 2 cells reacted with the fixative and consistently showed a dense content. However, the large granules in type 1 cells were mostly pale or less dense after this fixation. Two hours after intraventricular injection of 3H-dopamine, a large number of silver grains appeared only in the cytoplasm of intraventricular processes possessing dense core vesicles (type 2 cells). A few grains were also found in the perikarya. It is concluded that type 2 cells are catecholamine-storing cells. It is suggested that type 1 cells in the infundibular recess are peptidergic neurons which may secrete some hypothalamic regulating hormones of the anterior pituitary. Most of these cells in the preoptic recess belong to the neurosecretory cells of the preoptic nucleus, while some cells probably function similarly to those in the infundibular recess.