Hypertension in black patients: an emerging role of the endothelin system in salt-sensitive hypertension.

The prevalence of essential hypertension in blacks is much higher than that in whites. In addition, the pathogenesis of hypertension appears to be different in black patients. For example, black patients present with a salt-sensitive hypertension characterized by low renin levels.

ET-1 in the myocardial interstitium: relation to myocyte ECE activity and expression.

Increased plasma levels of endothelin-1 (ET-1) have been identified in congestive heart failure (CHF), but local myocardial interstitial ET-1 levels and the relation to determinants of ET-1 synthesis remain to be defined. Accordingly, myocardial interstitial ET-1 levels and myocyte endothelin-converting enzyme (ECE)-1 activity and expression with the development of CHF were examined. Pigs were instrumented with a microdialysis system to measure myocardial interstitial ET-1 levels with pacing CHF (240 beats/min, 3 wk; n = 9) and in controls (n = 14).

Distribution of endothelin receptors in saphenous veins of African Americans: implications of racial differences.

The relative density of endothelin-receptor subtypes A and B (ET(A) and ET(B), respectively) on endothelial and smooth muscle cells is the major determinant of the contractile response to endothelin-1 (ET-1). To investigate the effects of race on the distribution of ET receptors, the endothelin-receptor subtypes on membrane fractions prepared from saphenous veins obtained from African-American patients undergoing coronary bypass surgery were analyzed. Similar studies were repeated with endothelium-denuded samples to study the role of endothelium- and smooth muscle-derived ET(B) receptors.

Identification of amino acid residues in the C-terminal tail of big endothelin-1 involved in processing to endothelin-1.

Big endothelin-1 (big ET-1) is converted to 21-amino acid residue endothelin-1 (ET-1) via a specific cleavage at Trp21-Val22 by endothelin converting enzyme (ECE). This conversion is an essential step to produce bioactive ET-1 and represents a regulatory site in the biosynthesis of this potent vasoconstrictor. ECE-1a, a unique membrane-bound enzyme, processes big ET-1 more efficiently than other big ET isoforms, which mainly differ in the C-terminal tail (residues 22-38).

The effect of regulation of high blood pressure on plasma endothelin-1 levels in blacks with hypertension.

Plasma concentrations of immunoreactive endothelin-1 (irET-1) are significantly elevated in blacks with hypertension. In the present study, we investigated the effect of the regulation of high blood pressure on plasma irET-1 levels in black hypertensive individuals. After the initial blood samples were collected from 20 black patients with uncontrolled high blood pressure (Day 1), an intensive antihypertensive treatment was initiated, and the blood pressure and plasma irET-1 levels were monitored on days 2, 8, and 22.

Gender differences in the expression of endothelin receptors in human saphenous veins in vitro.

The contractile response to endothelin-1 (ET-1) appears to be modulated by the relative density of ETA and ETB receptors. To determine the effects of gender on the distribution of ET receptors, we analyzed the endothelin receptor subtypes on membrane fractions prepared from saphenous vein samples obtained from patients of different genders undergoing coronary artery bypass graft surgery. The contractile response to ET-1 in the presence and absence of 1 microM of the ETA receptor antagonist BQ-123 was also investigated.

Metabolism of endothelin-1 by neuroblastoma x glioma hybrid (NG108-15) cells.

The endothelin (ET) peptides, ET-1, ET-2, and ET-3, as well as the ETA and ETB receptor subtypes, are known to occur in brain, but there is a dearth of information on the metabolism of these peptides by the central nervous system (CNS). In this study we have investigated the kinetics of ET-1 binding to and dissociation from the hybrid neuroblastoma x glioma cell line, NG108-15, which is known to contain functional ET receptors, and metabolism of bound ET-1. [125I]ET-1 was incubated with cells for various periods of time up to 6 h, and the nature of the radioactivity in the cell medium and lysate was analyzed by reverse phase high performance liquid chromatography (HPLC).

Endothelin binding to NG108-15 cells: evidence for conventional ETA and ETB receptor subtypes and super-high affinity binding components.

The endothelin (ET) peptides have been identified in the CNS, but there is a paucity of information on their physiological roles. NG108-15 cells, a clonal strain of a neuroblastoma x glioma hybrid cell line, have been widely used in neurobiological research since they retain certain differentiated properties of the non-transformed parental cells. It is known that NG108-15 cells respond to the ET peptides, but only limited information is available on the characterization of the ET receptors that mediate these effects.

Endothelin degradation by vascular smooth muscle cells.

The mechanism(s) of degradation of the potent vasoconstrictor endothelin-1 (ET-1) by rat vascular smooth muscle A-10 cells, which possess the ETA receptor subtype, was investigated by incubating [125I]ET-1 (0.1 nM) with cells for 0-4 h at 37 degrees C in the presence and absence of lysosomal enzyme inhibitors, NH4Cl and chloroquine, and a neutral endopeptidase inhibitor, phosphoramidon. The assay buffer and cell extracts were analyzed by reverse-phase HPLC, and the radioactivity in the fractions was measured.

Racial differences in plasma endothelin-1 concentrations in individuals with essential hypertension.

Hypertension is more prevalent in blacks than whites, and the reasons for this difference remain unclear. To test whether endothelin may play a role in these racial variations, we analyzed plasma samples from black and white women and men with high blood pressure by an enzyme-linked immunoassay specific for endothelin-1 (ET-1), a potent vasoconstrictor, and compared them with those obtained from similar subjects with normal blood pressure. Both female and male hypertensive blacks had elevated levels of immunoreactive ET-1 (11.

Identification of receptor binding and activation sites in endothelin-1 by use of site-directed mutagenesis.

This study addresses the structural requirements for the intracellular processing and receptor binding properties of endothelin-1 (ET-1). Point mutants of preproendothelin-1 cDNA, with replacement of the codons for Lys9 of ET-1 by ones for Ala and Glu and of Ile20 and Trp21 by ones encoding Ala, were expressed in COS-7 cells. Competitive binding experiments on rat vascular smooth muscle cells (A-10), which were shown to be an ETA receptor-rich cell line, between [125I]ET-1 and synthetic ET-1, wild-type recombinant ET-1, and recombinant [Ala9]ET-1, [Glu9]ET-1, [Ala20]ET-1, and [Ala21]ET-1 yielded Ki values of 0.

Characterization of endothelin receptor subtypes on airway smooth muscle cells.

Endothelin-1 (ET-1) has constrictor and mitogenic effects on airway smooth muscle strips and cultured cells, respectively. This study addresses the type of the ET receptor subtype(s) present on ovine airway smooth muscle cells and the possibility of autocrine effects. The expression of the preproendothelin-1 gene was demonstrated by Northern analysis, and the medium obtained from these cells contained immunoreactive-ET-1.

Trp-21 is important in the processing and secretion of big endothelin-1.

To investigate the intracellular processing of endothelin-1 (ET-1), the synthesis and secretion of preproET-1 (PPET-1) was studied in transiently transfected COS-7 cells. Replacements at the highly conserved C-terminal region of ET-1 were made by site-directed mutagenesis, with codons for residues Ile-20 and Trp-21 being replaced by one for Ala in the PPET-1 cDNA. The mutant and wildtype PPET-1 cDNAs were expressed in COS-7 cells following transient transfection, and cell media and extracts, collected after 48 h, were assayed for ET-1 and big ET-1 by radioimmunoassay.

A transformed murine Leydig cell line expresses the ETA receptor subtype.

We recently demonstrated that transformed murine Leydig cells (MA-10) responded to endothelin-1 (ET-1) via increased steroidogenesis. This study addresses the endothelin receptor subtype present on this cell line and whether or not the cells produce ET-1. The expression of the preproendothelin-1 (PPET-1) gene was investigated by Northern blot analysis, and PPET-1 mRNA was found to be < 0.

Endothelin-1 promotes mitogenesis in airway smooth muscle cells.

Endothelin exists as three isoforms (ET-1, ET-2, and ET-3) and exhibits vasoconstricting, bronchoconstricting, and growth-promoting properties in vascular smooth muscle. In the airways, ET-1 immunoreactivity and mRNA have been detected and localized to the epithelium, smooth muscle, and endothelium in different species, including humans. It has been suggested that ET-1 may have a role in the airway smooth muscle hyperplasia and hypertrophy seen in patients with bronchial asthma.

Endothelin-1 promotes steroidogenesis and stimulates protooncogene expression in transformed murine Leydig cells.

The effects of endothelin-1 (ET-1), a potent vasoconstrictor and mitogen to various cell types, on proliferation and differentiated functions of the murine Leydig tumor cell line MA-10 were investigated. Kinetic binding experiments at room temperature showed that [125I] ET-1 bound to MA-10 cells and reached equilibrium in 2 h. The data from competitive binding experiments yielded an apparent single class of high affinity binding sites characterized by a Kd and maximum binding capacity of 1 nM and 59 fmol/10(6) cells, respectively.