Immunoreactive localization of vasoactive hormones (atrial natriuretic peptide and endothelin) in the heart of Protopterus annectens, an African lungfish

The present study demonstrated, by immunohistochemistry and Western blotting, the presence of immunoreacting atrial natriuretic peptide (ANP) and endothelin in the heart of Protopterus annectens by both light and electron microscopy. The distribution of ANP granules was investigated. ANP granules were localised in myocytes from the atrium, ventricle and conus arteriosus; endothelin-l (ET-1) was demonstrated in subendocardial myocytes of the atrium and the conus. No ET-1 immunoreactivity was observed in the ventricle wall. At the light-microscopical level, ET-1 appeared to occur in the endocardium, but at the electron-microscopic al level no immunogold labelling was seen on the granules of the endocardial cells. It is suggested that ET-1 is produced and stored in the subendocardial cells and re leased into the subendocardial space to reach the ANP-producing myocytes and the endothelial cells.