Specific binding of atrial natriuretic factor in brain microvessels.

Abstract

Cerebral capillaries constitute the blood-brain barrier. Studies of specific receptors (neurotransmitters or hormones) located on this structure can be performed by means of radioligand-binding techniques on isolated brain microvessels.We examined on pure bovine cerebral microvessel preparations the binding of atrial natriuretic factor (ANF), using 12I-labeled ANF. Saturation and competition experiments demonstrated the presence of a single class of ANF-binding sites with high affinity (dissociation constant, 10-10 M) and with a binding capacity of 58 fmol/mg of protein. The binding of 125I-labeled ANF to brain microvessels is specific, reversible, and time dependent, as is shown by association-dissociation experiments. The demonstration of specific ANF-binding sites on brain microvessels supposes a physiological role of ANF on brain microvasculature. The coexistence of ANF and angiotensin II receptors on this cerebrovascular tissue suggests that the two circulating peptides may act as mutual antagonists in the regulation of brain microcirculation and/or blood-brain barrier function. microcirculation and/or the permeability of the blood-brain barrier. MATERIALS AND METHODSMaterials. The nomenclature of atrial natriuretic peptides is based on the sequence of the propeptide containing 126 amino acids (rat y-ANF) deduced from the rat DNA sequence (9-11). Synthetic and biologically active rat ANF used in our study has the following sequence of 28 amino acids from Ser-99 to Tyr-126:Ile-Gly-Ala-Glu-Ser-Gly-Leu-Gly-Cys-Asn-Ser-Phe-Arg-Tyr-COOH . Mammalian atria contain different peptides, including the atrial natriuretic factor (ANF), that possess potent diuretic, natriuretic, and vasoactive properties (1,2). ANF is released into the general circulation and has been proposed to be actively involved in blood-pressure regulation and fluid homeostasis as an antagonist of the renin-angiotensin (Ang) system through receptor-mediated actions in the kidney (3), vascular tissues (4), adrenal glands (5), and brain (6). In the brain, binding sites for ANF have been characterized in specific areas involved in blood-pressure control, such as the subfornical organ (7)-a circumventricular structure that lacks the tight capillary endothelial junctions of the blood-brain barrier and, therefore, is exposed to circulating peptides. Recently, specific binding sites for Ang II have been described in brain microvessels (8) Methods. Isolation of bovine brain microvessels. Bovine brains were rapidly removed after sacrifice in a slaughterhouse and transported to the laboratory in an ice-cold box. Brain microvessels were isolated by the method of Goldstein et al. (12) with some modifications. The entire procedure was carried out at 4TC. After removal of the meninges by dissection, pieces of grey matter were scraped from the surface of the cerebral cortex. The tissues were minced and gently homogenized in gassed (95% 02/5% C02) Ringer's solution [137 mM NaCl/5 mM KCl/3 mM CaCl2/12 mM NaHCO3/15 mM Hepes/5 mM (+)-glucose] containing 1% fr...

Localization of 125I-atrial natriuretic peptide (ANP) in the rat fetus

“…In adults, ANP binds to the leptomeningeal surface of the brains and spinal cord (Mantyh et al 1987), where the hormone may play a role in regulating fluid/electrolyte exchange between blood vessels and the CSF. In addition, ANP binds to cerebral capillaries and may be involved with regulating microciruclation of the brain (Bianchi et al 1985;Chabrier et al 1987). Both the meninges and blood vessels are derived from the surrounding mesenthyme (Moore 1988).…”

Elevation by Atrial Natriuretic Factors of Cyclic GMP Levels in Astroglia‐Rich Cultures from Murine Brain

“…Although astroglia cells numerically dominate the astroglia-rich culture (Hallermayer and Hamprecht, 1984;Loffler et al, 1986), the possibility has to be considered that the ANF-induced changes take place solely in other, minor cell populations that are known to be present, such as oligodendrocytes, ependymal cells, and phagocytes, or in cells whose presence cannot be ruled out, e.g., capillary endothelial cells and pericytes. The latter two cell types especially would be a focus of interest, because brain microvessels have binding sites for rANP (Chabrier et al, 1987). Nevertheless, the possibility that the rise in the level of cyclic GMP occurs only in a minor cell population is less likely for two reasons: (a) The maximal levels of cyclic GMP found in the rat cultures are somewhat (a factor of 1.5-2) higher even than in the clonal rat glioma cell line C6-BU-1 (Friedl et al, 1986).…”

Thromboembolic complications in atrial fibrillation.

“…31 Atrial natriuretic peptide increases hematocrit, 32^3 as do paroxysms of AF. 34 Chabrier et al 35 found atrial natriuretic peptide receptors in the microvessels of the brain, and although the importance of this finding is unknown, there might be a relation between elevated atrial natriuretic peptide concentration, decreased cerebral blood flow, and the occurrence of cerebrovascular complications in patients with AF. 30 Studies relating the left atrial diameter to stroke risk have yielded conflicting results.…”