Endothelin-3 inhibits ganglionic transmission at preganglionic sites through activation of endogenous thromboxane A2 production in dog cardiac sympathetic ganglia

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Parasympathetic neurotransmission in rabbit isolated bronchus is modulated at prejunctional sites via endothelinB receptor stimulation

OBJECTIVE

The aim of this study was to investigate the mechanism involved in endothelin-induced potentiation of the response to parasympathetic nerve stimulation.

METHODOLOGY

We used autoradiographic and functional studies in rabbit isolated bronchi.

RESULTS

Autoradiography revealed dense binding sites for radiolabelled endothelin-3 over bronchial parasympathetic ganglia. The contractile response of the bronchus to electrical field stimulation was significantly potentiated by endothelin-3, endothelin-1, sarafotoxin S6c and BQ-3020 to 326+/-53%, 293+/-63%, 514+/-119% and 655+/-178%, respectively, of control values. The endothelin-3-induced potentiation of neurally evoked responses was not affected by the presence of propranolol, phentolamine or hexamethonium. The potentiation was also unaltered by pretreatment with the endothelinA receptor antagonist BQ-123 (3 micromol/L), but was significantly reduced in the presence of the combined endothelinA/endothelinB receptor antagonist PD 145065, indicating that the potentiation was mediated via endothelinB receptors. Confirmation of endothelinB receptor involvement in the neuropotentiation was obtained by demonstration of a significant amelioration of the potentiation in the presence of the endothelinB receptor selective antagonist BQ-788, and after endothelinB receptor desensitization by the endothelin, receptor selective agonist sarafotoxin S6b.

CONCLUSIONS

These results suggest that the endothelin-induced potentiation of parasympathetic neural responses in the rabbit bronchus is mediated via endothelinB receptor activation.

Physiological role of brain endothelin in the central autonomic control: from neuron to knockout mouse

Although endothelin (ET) was discovered as a potent vascular endothelium-derived constricting peptide, its presumed physiological and pathophysiological roles are now considered much more diverse than originally though. Endothelin in the brain is thought to be deeply involved in the central autonomic control and consequent cardiorespiratory homeostasis, possibly as a neuromodulator or a hormone that functions locally in an autocrine/paracrine manner or widely through delivery by the cerebrospinal fluid (CSF). This notion is based on the following lines of evidence. (1) Mature ET, its precursors, converting enzymes, and receptors all are detected at strategic sites in the central nervous system (CNS), especially those controlling the autonomic functions. (2) The ET is present in the CSF at concentrations higher than in the plasma. (3) There is a topographical correspondence of ET and its receptors in the CNS. (4) The ET is released by primary cultures of hypothalamic neurons. (5) When ET binds to its receptors, intracellular calcium channels. (6) An intracerebroventricular or topical application of ET to CNS sites elicits a pattern of cardiorespiratory changes accompanied by responses of vasomotor and respiratory neurons. (7) Recently generated knockout mice with disrupted genes encoding ET-1 exhibited, along with malformations in a subset of the tissues of neural crest cell lineage, cardiorespiratory abnormalities including elevation of arterial pressure, sympathetic overactivity, and impairment of the respiratory reflex. Definitive evidence is expected from thorough analyses of knockout mice by applying conventional experimental methods.