Endothelin-A-receptors in human aorta and pulmonary arteries are downregulated in patients with cardiovascular disease: an adaptive response to increased levels of endothelin-1?

Circulating levels of endothelin-1 (ET-1) are elevated in a number of pathophysiological conditions. Our aim was to determine the effect of overexpression of the peptide on ET receptors in human blood vessels. Aorta and pulmonary arteries were removed from patients with dilated cardiomyopathy (CDM), ischaemic heart disease (IHD), and primary pulmonary hypertension (PPH) and compared with controls. Sections of the medial (smooth muscle) layer were incubated with [125I]ET-1 and increasing concentrations of FR139317, an endothelin-A- (ET(A)) selective antagonist. FR139317 competed for the binding of iodinated ET-1 monophasically, indicating that all vessels examined expressed ET(A)-receptors in the media. ET(B)-receptors could not be detected, either in the control vessels or in those from patients with disease. There was no change in affinity (K(D)) but there was a significant (*p < 0.05) reduction in ET(A)-receptor density (Bmax) by 20-50% in diseased tissues, compared with controls. These results suggest that ET(A)-receptors are downregulated as an adaptive response to increased levels of ET-1.