VASOCONSTRICTOR ENDOTHELIN RECEPTORS CHARACTERIZED IN HUMAN RENAL-ARTERY AND VEIN IN-VITRO

1 We have identified the endothelin receptors present in the media of human main stem renal artery and vein and characterized the subtypes m ediating vasoconstriction in these blood vessels in vitro. 2 Messenger RNA encoding both ET(A) and ET(B) receptors was identified in the smo oth muscle layer of human renal artery and vein by reverse transcripta se-polymerase chain reaction assay. In cryostat-cut cross-sections of both vessels autoradiographical visualisation suggested a majority of ET(A) receptors. Intense binding was obtained to the non-selective lig and [I-125]-ET-1 and the ET(A)-selective [I-125]-PD151242 but only wea k labelling of sites by the ET(B)-selective [I-125]-BQ3020. 3 ET-1 pot ently constricted renal artery and vein preparations with EC(50) value s of 4.06 nM and 1.00 nM, respectively. Sarafotoxin 6b was approximate ly ten times less potent than ET-1 with EC(50) values of 36.3 nM and 1 3.8 nM respectively. In the renal artery, ET-3 and sarafotoxin 6c show ed little or no activity up to 300 nM. Responses to these peptides wer e more variable in the renal vein. Preparations from three individuals did not respond to ET-3 but in three further cases, although ET-3 was much less potent than ET-1, full dose-response curves were obtained. S6c elicited dose-related contractions in vein preparations from 5/6 i ndividuals and although more potent than ET-1, the maximum response wa s 30-60% of that obtained to ET-1. 4 ET-1-induced vasoconstriction of renal artery and vein was antagonized by the ET(A)-selective, BQ123 (3 -10 mu M). The dose-response curves to ET-1 were displaced in a parall el rightward fashion with no attenuation of the maximum responses, pA( 2) values were estimated to be 6.8 +/- 0.1 and 6.8 +/- 0.4 for artery and vein respectively. 5 These data suggest that mRNA encoding both ET (A) and ET(B) receptors is present in the media of human main stem ren al artery and vein. However, autoradiographical studies indicate that the majority of ET receptors expressed are of the ET(A) subtype. The r elative potencies of ET-1 and ET-3 as vasoconstrictors of renal blood vessels in vitro is consistent with this being an ET(A)-mediated respo nse, and therefore whilst responses to S6c indicate that constrictor E T(B) receptors may be present in renal veins from some individuals the se are likely to be of less importance in these blood vessels.