Selective downregulation of ET(A) receptor mRNA in renal transplant recipients on cyclosporin A revealed by quantitative RT-PCR

Despite intensive investigation, a pathophysiological role for the endogenous vasoconstrictor peptide endothelin (ET) remains elusive. The kidney is particularly sensitive to the effects of ET, which are mimicked by the administration of cyclosporin A (CsA), and animal models suggest a role for ET in the vasoconstricive effects of CsA. Using a recently validated novel fluorescent quantitative RT-PCR assay to enable the direct study of human renal biopsies, we have quantified mRNA for the two known ET receptor subtypes ET(A) and ET(B) in cortical tissue from three groups of patients: renal transplant recipients on CsA (n = 7), those with native renal disease (n = 5) and normal controls (n = 7). Median mRNA levels (amol/mu g total RNA) were 0.024, 0.17 and 0.2 respectively for ET(A) and 0.57, 0.64 and 0.96 for ET(B). These values indicate significant downregulation of ET(A) (P = 0.003) but not ET(B) (P = 0.104) mRNA in the transplant group. These results provide the first demonstration of a perturbation in the human ET system at tissue level in a pathophysiological situation, and suggest that the deleterious renal vasoconstrictor effects of CsA might be ameliorated by selective ET(A) receptor antagonism in the future. This study also illustrates the feasibility of ex vivo analysis of human diagnostic material at the molecular level.