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Hypertension. 2000 Mar;35(3):726-31.

ET(B) receptor blockade potentiates the pressor response to big endothelin-1 but not big endothelin-2 in the anesthetized rabbit.

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  • 1Department of Pharmacology, Yale University School of Medicine, Boyer Center for Molecular Medicine, New Haven, CT, USA.

Abstract

The precursor of endothelin-1, big endothelin-1, is considered to be a more reliable marker of systemic production of vasoactive peptide. However, it is largely unclear whether ET(B) receptor-dependent clearance and endothelium-derived relaxing factors affect the precursor in a similar manner to mature ET-1. These ET(B)-dependent modulations of big ET-1 and big ET-2 pressor properties were therefore studied in the anesthetized rabbit. When injected into the left cardiac ventricle, ET-1 and ET-2 (0.01 to 1 nmol/kg) each induced biphasic responses (a depressor followed by a pressor response), whereas big ET-1 and big ET-2 (0.1 to 3 nmol/kg) caused only protracted pressor responses. The highest dose of big ET-1 caused significantly greater responses than ET-1, ET-2, or big ET-2. A selective ET(A) receptor antagonist, BQ-123 (1 mg/kg), markedly reduced pressor responses to all 4 peptides, whereas blockade of ET(B) receptors with BQ-788 (0.25 mg/kg) sharply potentiated the responses to ET-1, ET-2, and big ET-1, but not to big ET-2. Indomethacin (10 mg/kg) sharply potentiated the pressor response to ET-1 (1 nmol/kg), but not big ET-1, at all time points. In control animals, ET-1, but not big ET-1, also triggered an indomethacin-sensitive increase in circulating prostacyclin. Finally, systemically administered big ET-1, but not big ET-2, induced a phosphoramidon-sensitive increase in plasma IR-ET. Our results suggest a significant limiting role of ET(B) receptors on pressor responses to big ET-1. In contrast, the same receptor entities do not modulate the hemodynamic properties of the ET-2 precursor, given that, unlike big ET-1, it is poorly converted in the pulmonary or systemic circulation in anesthetized rabbits.

PMID:
10720586
[PubMed - indexed for MEDLINE]
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