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The natriuretic peptide system in the brain: implications in the central control of cardiovascular and neuroendocrine
Abstract:
The natriuretic peptide system consists of three endogenous ligands, i.e., atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), and at least three subtypes of receptors. All of the peptides and receptors exist in the central nervous system (CNS). ANPs in the brain are N-terminally truncated forms: ANP (4-28) and ANP (5-28). The primary structure of BNP varies considerably among species, whereas that of CNP is highly conserved. ANP, BNP, and CNP are distributed in discrete brain regions, although the distribution varies in different species. Few immunohistochemical studies have so far been performed on BNP and CNP. There are three subtypes of receptors: ANP-A and ANP-B, which are bioactive, and the C receptor, which does not seem to be directly related to bioactivity. In the rat, the major subtype of ANP receptor in the CNS is the ANP-B receptor, based on the results of Northern blotting. Since the ligand for ANP-B receptor is CNP, the CNP-ANP-B receptor system may be most important, at least in rat brain. It is still unknown whether or not a specific receptor for BNP exists in central or peripheral tissues. Further studies should clarify the exact localization of ANP, BNP, and CNP and the three receptor subtypes in the CNS. Although natriuretic peptides and their receptors are distributed widely in the CNS, the AV3V regions, basal medial hypothalamus, brainstem, and circumventricular organs are the most prominent sites. This suggests an important physiological role of the natriuretic peptide system in the central control of cardiovascular homeostasis. The natriuretic peptide system seems to be involved in the regulation of water and salt intake, blood pressure, and secretion of vasopressin in the direction of reducing body fluid and lowering blood pressure. Such actions of natriuretic peptides are antagonistic to the central actions of angiotensin II (AII). In fact, the distribution of ANP and AII and their receptors in the CNS overlaps considerably. It is highly likely, therefore, that the central natriuretic peptide system and the renin-angiotensin system play important roles in the central control of cardiovascular and body fluid homeostasis in opposite directions. The natriuretic peptide system may also be involved in neuroendocrine control and some other CNS functions, although the physiological significance of these actions is less clear at the present time. It is now clear that there is considerable plasticity in the regulation of natriuretic peptides and their receptors.(ABSTRACT TRUNCATED AT 400 WORDS)