Vol. 284, Issue 3, 895-903, March 1998

Endothelin_B Receptors in Rabbit Pulmonary Resistance Arteries: Effect of Left Ventricular Dysfunction¹

Cheryl C. Docherty and Margaret R. Maclean

Clinical Research Initiative in Heart Failure, Division of Neuroscience and Biomedical EC₅₀ Systems, Institute of Biomedical pEC₅₀ and Life Sciences, University of Glasgow, Glasgow, Scotland

The endothelin (ET) receptor that mediates vasoconstriction of the isolated rabbit pulmonary resistance artery was characterized using selective ET receptor agonists and antagonists. We also examined changes in ET-induced vasoconstriction brought about by left ventricular dysfunction using the rabbit coronary ligation model. The rank order of potency for contraction was sarafotoxin S6c (S6c) > ET-1 = ET-3, which is characteristic of an ET_B-like receptor. The combined ET_A/ET_B receptor antagonist SB209670 (1 µM) antagonized responses to ET-1 and S6c with estimated pK_b values of 6.8 ± 0.2 and 7.8 ± 0.2, respectively. BQ788 (1 µM) antagonized responses to S6c and ET-3 (but not ET-1) with estimated pK_b values of 7.1 ± 0.2 and 6.6 ± 0.1, respectively. The ET_A receptor antagonist FR139317 (1 µM), either alone or in combination with BQ788, did not inhibit responses to ET-1. The profile of the ET-1 response was not altered by left ventricular dysfunction. In control rabbits, the inhibitor of nitric oxide synthase N-nitro-L-arginine methyl ester (100 µM) had no significant effect on the potency of either ET-1 or S6c. In the coronary-ligated rabbits, however, it significantly increased the potency (10-15-fold) of both ET-1 and S6c. These results suggest that the ET receptor that mediates contraction in rabbit pulmonary resistance arteries has the characteristics of an ET_B-like receptor. The responses to ET-1 are not altered by LVD but may be modified by increased release of nitric oxide.