Selective downregulation of endothelin-B receptors in diabetic African-American patients

The purpose of this study was to investigate whether there are differences in the expression of the endothelin (ET) system in the peripheral vasculature of diabetic African-American (AA) and Caucasian (CA) patients. Tibial artery specimens were obtained from diabetic (AAD = 8 and CAD = 5) and non-diabetic (AAND = 6 and CAND = 5) patients undergoing lower limb amputation. The gene expression of ET-1 precursor (PPET-1), ET_AR and ET_BR was determined by a reverse transcriptase polymerase chain reaction technique. PPET-1 and ET_AR expression was up-regulated 4- and 3-fold, respectively, in both AA and CA diabetics (P<.05 vs non-diabetics). ET_BR mRNA was significantly lower in AA diabetic patients. Function of ET-1 and ET receptors was assessed by vascular contractility assays. Vascular relaxation in response to sodium nitroprusside in arteries precontracted with ET-1 was significantly lower in AA (58% ± 9) as compared to CA diabetics (74% ± 5) (P<.05). In conclusion, this study demonstrated that the ET system is altered in favor of the contractile phenotype in AA diabetics and may contribute to the increased incidence of vascular complications in this population.