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  • Title: Disproportionate decrease in alpha- compared with beta-adrenergic sensitivity in the dorsal hand vein in pregnancy favors vasodilation.
    Author: Landau R, Dishy V, Wood AJ, Stein CM, Smiley RM.
    Journal: Circulation; 2002 Aug 27; 106(9):1116-20. PubMed ID: 12196338.
    Abstract:
    BACKGROUND: Altered vascular responses to adrenergic agonists during pregnancy are thought to play an important role in the regulation of blood pressure and placental blood flow. Because alpha1-adrenergic and beta2-adrenergic sensitivity act in opposing directions to determine vascular tone, we simultaneously evaluated alpha-adrenergic-mediated vasoconstriction and beta-adrenergic-mediated vasodilation in dorsal hand veins during and after pregnancy. METHODS AND RESULTS: Twenty healthy pregnant women were studied at 32 to 37 weeks of gestation and again 12 weeks after delivery. Vascular response to phenylephrine (PE) and isoproterenol (ISO) was measured in a dorsal hand vein using the linear variable differential transformer technique. The dose of PE resulting in 50% constriction (CD50) was determined. The response to ISO was measured after the PE preconstriction. Pregnant and postpartum values, expressed as geometric mean (95% CI), were compared by paired t test. alpha-Adrenergic sensitivity during pregnancy (CD50 2.7 micro g/min [95% CI, 1.5 to 5.0]) was markedly decreased, approximately 7-fold, compared with postpartum (0.4 micro g/min [95% CI, 0.3 to 0.7] [P<0.01]). beta-Adrenergic vasodilation was also attenuated during pregnancy. The ED50 of ISO (dose of ISO resulting in 50% of the maximal response, E(max)) was greater during pregnancy (20 ng/min [95% CI, 11 to 35]) than postpartum (8 ng/min [95% CI, 5 to 12]) (P<0.05). ISO E(max) was also significantly less during pregnancy (81% [95% CI, 65 to 97] compared with postpartum (105% [95% CI, 97 to 113]) (P<01.01). CONCLUSIONS: Normal pregnancy is characterized by decreased venous sensitivity to both alpha1-adrenoceptor-mediated vasoconstriction and beta2-adrenoceptor-mediated vasodilation. The greater decrease in alpha1 compared with beta2 response may contribute to the vasodilated state characteristic of human pregnancy.
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