Human umbilical vein vasoconstriction induced by epinephrine acting on α1B-adrenoceptor subtype

Objective Our purpose was to determine the presence of α1-adrenoceptor messenger RNA subtypes and extend the pharmacologic characterization of α1-adrenoceptors involved in human umbilical vein (HUV) contraction. Study design Cords (n = 124) from healthy patients after term vaginal or cesarean deliveries were used. The vein was carefully dissected out of cords and used for reverse transcription combined with polymerase chain reaction (RT-PCR) to amplify α1-adrenoceptor transcripts. In isolated organ baths, HUV rings were mounted and cumulative concentration-response curves were constructed either for epinephrine or the selective α1A-adrenoceptor agonist, A-61603. In other series of experiments, the effects of the selective α1A- and α1B-adrenoceptor antagonists (RS-100329 or B8805-033 or spiperone, AH11110A and cyclazosin, respectively) were evaluated to estimate its blocking potencies on epinephrine concentration-response curves. Results By means of RT-PCR technique α1a- and α1b-adrenoceptor transcripts were detected in the HUV. The blocking potency values of RS-100329 or B8805-033 against responses mediated by epinephrine were not consistent with the activation of an α1A-adrenoceptor population. Moreover, the low potency of the agonist A-61603 was not in accordance with an α1A-adrenoceptor interaction. On the other hand, the antagonist potencies of spiperone, AH11110A and cyclazosin were in agreement with an interaction on α1B-adrenoceptor subtype. Conclusion Although α1a- and α1b-adrenoceptor messenger RNAs are detected in the HUV, only α1B-adrenoceptors are involved in epinephrine vasoconstrictor action