Although activation of the endothelin (ET) system contributes to pulmonary hypertension, modifications of the cardiopulmonary ET system and its responses to chronic ET receptor blockade are not well known. To investigate this, rats were injected with monocrotaline (60 mg/kg intraperitoneal) or saline, followed with treatment with the selective ET A receptor antagonist LU135252 (LU; 50 mg·kg -1 ·day -1 ) or with saline. After 3 weeks, haemodynamics, cardiac hypertrophy, ET-1 levels and cardiopulmonary ET-receptor-binding profile were evaluated. Monocrotaline ( n =7) elicited marked pulmonary hypertension and right ventricular hypertrophy compared with controls ( n =8). Both variables were substantially attenuated by LU therapy ( n =8; P <0.05 for both). After monocrotaline, right ventricular ET-1 levels were more significantly increased than in the left ventricle (+198% compared with +127%; P <0.05). ET B receptor density was augmented (3-fold) in the right ventricle, whereas that of ET A receptors was not affected. LU treatment also significantly attenuated these alterations ( P <0.05). In the lungs, ET-1 levels were not increased after monocrotaline, whereas the balance of ET B to ET A receptors was altered, with a trend toward a lower percentage of ET B than in the control rats. LU treatment did not affect these variables in the lungs. Therefore monocrotaline-induced pulmonary hypertension and right ventricular hypertrophy are associated with the up-regulation of ET-1 and ET B receptors in the right ventricle. These alterations are attenuated with the reduction of pulmonary hypertension and right ventricular hypertrophy after chronic blockade of the ET A receptors, supporting the role of the ET system in right ventricular hypertrophy.

The endothelins (ETs) stimulate the secretion of arginine-vasopressin (AVP) in vivo and in vitro . The activation of hypothalamic ET B receptors increases AVP release, but the neurotransmitters mediating these responses are not known. In the compartmentalized hypothalamo–neurohypophysial explant model, the overall basal release of AVP was 53±17pg·h -1 ·PP -1 (where PP is posterior pituitary). ET B receptor activation in hypothalamic sites by 1nM IRL1620 dose-dependently increased AVP secretion, with a maximal response of 340±70% of basal·h -1 ·PP -1 , whereas 1nM ET-1, the ET A receptor-selective agonist, inhibited AVP release to 44±8%·h -1 ·PP -1 . Addition of MK801 along with IRL1620 inhibited AVP release to a value no different from basal (122±41%·h -1 ·PP -1 ). In contrast, 10 µ M DNQX [6,7-dinitroquinozaline-2,3-(1 H ,4 H )-dione] did not block ET B receptor-induced AVP release (326±73%·h -1 ·PP -1 ), and nor did non-selective α-adrenergic receptor antagonism. The GABA A (where GABA is γ-aminobutyric acid) receptor agonist muscimol (10 µ M) inhibited AVP release in response to IRL1620 (127±30%·h -1 ·explant -1 ). These data suggest that AVP release induced by activation of hypothalamic ET B receptors is mediated by a hypothalamic N -methyl-D-aspartate (NMDA) receptor-mediated mechanism. In turn, the local release of GABA associated with NMDA activation may exert an inhibitory influence and dampen the AVP secretory response.

Cardiac preload reduction through venodilatation is beneficial in chronic heart failure. The recent development of endothelin receptor antagonists for possible therapeutic use in heart failure has hastened the need for a clearer understanding of the venoconstrictor actions of endothelin-1 in this disease. Two main subtypes of endothelin receptor, ET A and ET B , exist in human blood vessels. We studied the venoconstrictor effects of endothelin-1 (a non-selective ET A and ET B agonist) and sarafotoxin S6c (a selective ET B agonist) in vivo in patients with chronic heart failure and in age-matched healthy controls. On separate days at least 1 week apart, locally active doses of endothelin-1 or sarafotoxin S6c were infused into a suitable dorsal hand vein for 1 h, and the venous internal diameter was measured using a displacement technique. Venoconstriction in response to endothelin-1 was significantly blunted in heart failure patients compared with controls (26±7% and 51±6% peak reduction in vein calibre respectively; P = 0.013). Venoconstriction to sarafotoxin S6c was similar in heart failure patients and controls (17±5% and 17±4% peak reduction in vein calibre respectively). Both ET A and ET B receptors mediate venoconstriction in healthy subjects and in patients with chronic heart failure. Optimal inhibition of the venoconstrictor effects of endothelin-1 in chronic heart failure may therefore require administration of an antagonist with ET A - and ET B -receptor-blocking properties. Chronic heart failure may be associated with a selective decrease in venous ET A receptor sensitivity, but further studies are required to clarify the functional significance of this observation.

1. In the present study we investigated, first, the effects of high Na + intake and, second, the effects of water deprivation on plasma endothelin-1 concentration and urinary endothelin-1 excretion and on endothelin receptors in membranes of renal glomeruli and papillae and of aortic smooth muscle and lung tissue from 32 female Sprague-Dawley rats. 2. After 5 weeks of high Na + intake ( n = 8) urinary Na + excretion was 10.5 + 1.3 compared with 1.6 + 0.2 mmol/24h in controls. Body weight, plasma osmolality, plasma endothelin-1 concentration (23 + 6 versus 28 + 3 fmol/ml) and urinary endothelin-1 excretion (6.1 + 13 versus 4.7 + 0.3 pmol/24 h) remained unchanged. 3. The characteristics of endothelin-1 receptors in glomeruli, papillae, aortic smooth muscle and lung tissue from salt-loaded rats were not different from those of controls. 4. After 48 h water deprivation ( n = 8) body weight had decreased, whereas packed cell volume and plasma and urine osmolalities had increased compared with controls ( n = 8) ( P <0.05). Plasma endothelin-1 concentration (40 + 6 versus 21 + 2 fmol/ml) was higher ( P <0.01) and urinary endothelin-1 excretion (1.0 + 0.2 versus 2.8 + 03 pmol/24 h) was lower than in controls ( P <0.01). 5. Water deprivation was accompanied by increases in endothelin-1 binding sites in glomeruli ( B max. 4.8 + 0.4 versus 3.6 + 0.2 pmol/mg of protein; P <0.05) with unchanged receptor affinity ( K d 56 + 9 versus 57 + 8 pmol/l), in papillae ( B max . 8.0 + 0.7 versus 6.2 + 0.5 pmol/mg of protein; P <0.05) with unchanged K d (78 + 6 versus 63 + 4 pmol/l) and in aortic smooth muscle cells ( B max. 3.5 + 0.2 versus 2.8 + 0.2 pmol/mg of protein; P <0.05) in which K d rose to 307 + 27 versus 180 + 22 pmol/l ( P <0.05). Endothelin-1 receptors in lung tissue were unaltered ( B max . 10.0 + 03 versus 103 + 0.8 pmol/mg of protein; K d 152 + 12 versus 137 + 14 pmol/l). 6. Our results suggest that the peripheral endothelin-1 system may play a role in the adaptation to changes in body water content rather than in Na + balance.

1. A peptide-protein mobility shift assay has been developed, using native polyacrylamide-gel electrophoresis, that enables the isolation of de-natured receptor proteins from small amounts of human cardiac tissue. 2. Radiolabeled endothelin-1 and related peptides were used to identify and isolate endothelin receptors from partially purified membrane extracts of human atrial tissue. 3. Binding analysis using radiolabelled endothelin-1 gave an equilibrium dissociation constant ( K d ) of 2 nmol/l, similar to results from binding experiments conducted directly on tissue. 4. Peptide-receptor complexes were electroeluted from native gels and dissociated. Receptor material was characterized by dot-immunobinding analysis of eluates using an antibody raised against a predicted human endothelin receptor sequence.