Coronary vasoconstriction in vitro in the hearts of polyarthritic rats: effectiveness of in vivo treatment with the endothelin receptor antagonist SB 209670

Investigation into the potential anti-inflammatory effects of endothelin antagonists in a murine model of experimental monosodium urate peritonitis

Endothelin (ET)-1 has been detected in many inflammatory pathologies, including rheumatoid arthritic patients, asthma, and ischemic-reperfusion injury. In this study, we have investigated the effect of a panel of different ET-1 antagonists displaying different selectivities for the receptors in a murine model of experimental inflammatory peritonitis. Systemic treatment of mice with the ETA antagonist C33H44N6O5, N-[N-[-N(hexahydro-1H-azepin-1-yl)carbonyl]-L-leucyl]-1-methyl-D-tryptophyl]-3-(2-pyridinyl)-D-alanine (FR139317) inhibited neutrophil accumulation. However, a greater degree of inhibition was observed with the ETB antagonist C34H51N5O7, N-cis-2,6-dimethylpiperidinocarbonyl-b-tBu-Ala-D-Trp(1-methoxycarbonyl)-D-Nle-OH (BQ-788) and the ET(A and B) antagonist C52H65N7O10, N-acetyl-alpha-[10,11-dihydro-5H-dibenzo-[a,d]cycloheptadien-5-yl]-D-Gly-Leu-Asp-lle-lle-Trp (PD145065); all these effects occurred without altering peripheral blood cell counts. Release of the CXC chemokine KC was significantly reduced by the FR139317 and PD145065 but not by BQ-788. Evaluation of the therapeutic potential of these antagonists showed that PD145065 inhibited neutrophil migration and KC release, whereas the others caused a nonsignificant reduction in these parameters. Parameters of endothelial cell activation showed that urate-stimulated interleukin-1beta release was inhibited by BQ-788 and PD145065 but not by FR139317, whereas ET-1 was only inhibited by the mixed antagonist. A different scenario was observed with respect to release of the CXC chemokine KC with FR139317 and PD145065 being effective, whereas with a marker of polymorphonuclear activation the ETA and mixed antagonist inhibited adhesion molecule expression. These data show that ET-1 antagonists elicit different mechanisms of actions in the way they display their antimigratory effects in a murine model of monosodium urate crystal peritonitis.

What turns on the endothelins?

Production of the potent vasoconstrictor peptide endothelin-1 (ET-1) within the circulation is increased markedly in a number of pathologies, such as the damage following from ischaemia and reperfusion, vasculitis, congestive heart failure, and systemic inflammatory response (septic shock syndrome) and related pathological states. All these conditions are associated with marked increases in the production of cytokines such as tumour necrosis factor-alpha and interleukin-2. Our experiments indicate that in rats administration of either of these cytokines results in a rapid increase in the circulating levels of ET-1 and a very pronounced ET-1-dependent coronary vasoconstriction. Furthermore, in rats suffering from adjuvant polyarthritis, in which there is marked joint inflammation and associated cytokine production, there are dramatic increases in coronary perfusion pressure which are absent when rats are treated with an endothelin receptor antagonist. This does not imply that inflammation must be associated with coronary vasoconstriction and myocardial dysfunction, but rather that in the rat, where ET-1 is a strong and almost irreversible constrictor of coronary vessels, coronary perfusion pressure serves as a very good bioassay for ET-1 activity. What our results do imply is that the ET-1 system is latent, but that in numerous disease states it can become rapidly upregulated following endothelial activation by cytokines.

The contribution of tumour necrosis factor-alpha and endothelin-1 to the increase of coronary resistance in hearts from rats treated with endotoxin

1. Inflammatory disease states predispose to myocardial infarction. Here we have investigated the effects of a systemic inflammatory response syndrome, i.e. lipopolysaccharide (LPS)-induced circulatory shock in rats, on coronary vascular tone. 2. Anaesthetized rats were given LPS (10 mg kg-1, i.v.) and the hearts excised 180 min later for isolated perfusion at constant flow by the Langendorff technique. Once the ex vivo perfusion was started, the perfusion pressure strongly increased in these hearts compared to hearts from control rats (130 +/- 3 vs. 49 +/- 3 mmHg after 10 min). This increase in coronary resistance was not associated with a reduction in endothelial cell function, for the vasodilator responses to bradykinin were unchanged. 3. When hearts were removed 30 min after the injection of LPS, the LPS-induced rise in perfusion pressure was delayed. No changes in perfusion pressure were seen when the hearts were removed 15 min after the injection of LPS. Pre-treatment with cycloheximide or an anti-tumour necrosis factor-alpha (TNF-alpha) antibody or continuous infusion in vivo and in vitro of the endothelin ETA receptor selective antagonist FR 139317, greatly decreased the increase in coronary vascular resistance induced by LPS. 4. These data suggest that TNF-alpha may induce the release of endothelin-1 (ET-1) and that this mediates at least part of the coronary vasoconstriction. This hypothesis is supported by the demonstration that LPS administration increased the circulating levels of both TNF-alpha and ET-1. 5. We conclude, therefore, that in inflammatory disease states, such as LPS-induced septic shock, there is the sequential release of TNF-alpha and endothelin-1 which leads to an increase in coronary vascular tone and so a predisposition to myocardial ischaemia. Inactivation of TNF-alpha by an antibody as well as ETA receptor blockade by a selective antagonist may effectively interfere with this pathway.