Brain natriuretic peptide(BNP) is a recently discovered novel neuropeptide of 26 amino acid residues, isolated from porcine brain, that is of similar potency to atrial natriuretic factor(ANF) in natriuretic, diuretic, hypotensive and smooth muscle relaxant activities. we used a highly selective antisera against BNP raised in rabbit to observe its distribution and localization in some brain areas and some other peripheral tissues by utili zing high sensitive avidin-biotin-peroxidase complex technique. Positive brain natriuretic peptide immunoreactive (BNPir) fibers and cell bodies were observed in the lateral hypothalamic area, caudate-putamen, hippocampus, amygdala, and supraoptic and paraventricular nuclei. A lot of BNPir granules were also found in rat atria. They were of similar localization to that of ANF. Most of the specific granules were accumulated in cytoplasm at both nuclear poles of atrial myocytes. The BNP immunoreactivity is less intense than that of the ANF. Some of scanty, diffuse and fine BNPir granules could also be observed in ventricular myocytes.The coexistence of both BNP and ANF in the brain and heart indicates that BNP may function as a neuropeptide and circulating hormone, and suggests the possibility that the physiological effects such as diuretic natriuretic, hypotensive and smooth muscle relaxant activities so far thought to be mediated by ANF may be regulated through a dual mechanism involving both BNP and ANF. In addition, some BNPir positive cells were also present in the anterior and intermediate lobes of rat pituitary gland. The significance of BNP in hypophysis would be elucidated in the further studies.

Endothelin (ET), recently isolated from culture supernatant of porcine aortic endothelial cells, is a novel potent vasoconstrictive substance. In this paper a highly specific rabbit antisera against endothelin was used to study the localization of ET in the isolated endothelial cells, from human umbilical veins and porcine arota, and that of ET in the cryostat cross sections of porcine aorta by using ABC immunohistochemical technique. The results demonstrate that a varied amounts of specific ET-like immunoreactive substance exist in the endothelial cytoplasm of human umbilical veins and porcine aorta which provides the mor- phological evidence for elucidating the endocrine function of vascular endothelial cells.