α_1A- and α_1B-adrenoceptors are the major subtypes in human saphenous vein

In this study we analyzed the different α₁-adrenoceptor (AR) subtypes present in human saphenous vein (HSV) using reverse transcription polymerase chain reaction (RT-PCR), DNA-DNA hybridization analysis and functional affinities for α-AR antagonists. DNA-DNA hybridization analysis of RT-PCR amplification products confirmed the presence of α_1A- and α_1B-ARs, and low levels of α_1D-AR in HSV. The functional results showed: (1) prazosin, the selective α₁-AR antagonist, phentolamine, the α₁- and α₂-ARs antagonist, WB 4101 and 5-MU, the selective α_1A-AR subtype antagonists were potent, competitive antagonists of noradrenaline (NA)-induced contraction (pA₂ values of 11.03, 8.06, 9.02 and 8.34, respectively). (2) α₁-AR-induced contraction was sensitive to the alkylating effects of CEC (the α_1B and α_1D-AR subtypes antagonist) and (3) The selective α_1D-AR subtype antagonist BMY displayed low affinity (pA₂ values of 6.44). This indicates that the contractile response of the HSV to α₁-AR-induced is predominantly mediated by both α_1A and α_1B-AR subtypes. This was also supported by the good relationship between pA₂ values from the present study and reported binding affinities (pK_i) values of various α₁-AR subtype antagonists with cloned human α_1A- and α_1B-AR subtypes (r=0.89 and r=0.98, respectively), but not the α_1D-AR subtype (r=0.67). Our results indicate that α_1A- and α_1B-ARs are the main functional and expressed receptor subtypes in HSV.