Reduced endogenous endothelin-1-mediated vascular tone in chronic renal failure

Background. Endothelin-l generated by the vascular endothelium contributes to basal vascular tone and blood pressure in healthy humans. Plasma concentrations of endothelin-l, which are elevated in chronic renal failure (CRF), may contribute to increased vascular tone. Methods. We investigated the contribution of endogenous and exogenous endothelin-l to the maintenance of vascular tone in patients with CRF (creatinine greater than or equal to 200 mu mol/liter) and in age- and sex-matched healthy subjects. In a series of experiments, we measured forearm vascular responses to intra-arterial norepinephrine (30 to 240 pmol/min), endothelin-l (5 pmol/min), the selective endothelin A (ETA) receptor antagonist BQ-123 (3 mg/hr), the mixed endothelin-converting enzyme and neutral endopeptidase inhibitor phosphoramidon (30 nmol/min), and the selective neutral endopeptidase inhibitor thiorphan (30 nmol/min). Results. The maximum reduction in forearm blood flow (FBF) to norepinephrine in CRF (33 +/- 7%) was similar to that in controls (43 +/- 7%, P = 0.53). Endothelin-l also produced a similar reduction in FBF in CRF (35 +/- 6%) and controls (36 +/- 5%, P = 0.81). BQ-123 increased FBF in CRF (11 +/- 4%) but significantly less than in controls (44 +/- 10%, P = 0.02). Phosphoramidon increased FBF in CRF (68 +/- 20%), again significantly less than in controls (181 +/- 41%, P = 0.001). Thiorphan reduced FBF similarly in CRF (22 +/- 6%) and controls (14 +/- 6%, P = 0.39). Responses to phosphoramidon were substantially greater than to BQ-123. Conclusions. These studies show that endogenous generation of endothelin-l contributes to the maintenance of resting vascular tone in patients with CRF, as well as in healthy subjects. Although the contribution of endogenous endothelin-l to resting vascular tone appears to be reduced in CRF, ETA receptor antagonism, and particularly endothelin-converting enzyme inhibition, should be explored as means by which to reduce vascular tone and blood pressure in patients with CRF.