Human umbilical vein vasoconstriction induced by epinephrine acting on alpha1B-adrenoceptor subtype

Objective: Our purpose was to determine the presence of alpha(1)-adrenoceptor messenger RNA subtypes and extend the pharmacologic characterization of alpha(1)-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 alpha(1)-adrenoceptor transcripts. In isolated organ baths, HUV rings were mounted and cumulative concentration-response curves were constructed either for epinephrine or the selective alpha(1A)-adrenoceptor agonist, A-61603. In other series of experiments, the effects of the selective alpha(1A)- and alpha(1B)-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 alpha(1a)- and alpha(1b)-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 alpha(1A)-adrenoceptor population. Moreover, the low potency of the agonist A-61603 was not in accordance with an alpha(1A)-adrenoceptor interaction. On the other hand, the antagonist potencies of spiperone, AH11110A and cyclazosin were in agreement with an interaction on alpha(1B)-adrenoceptor subtype.

Conclusion: Although alpha(1a)- and alpha(1b)-adrenoceptor messenger RNAs are detected in the HUV, only alpha(1B)-adrenoceptors are involved in epinephrine vasoconstrictor action.