Forearm vasodilator responses to a β-adrenergic receptor agonist in premenopausal and postmenopausal women

Beta-adrenergic vasodilator responses may be blunted in humans who are at an increased risk for hypertension. Because menopause is associated with an increase in blood pressure, we tested the hypothesis that forearm blood flow responses to the β-adrenergic receptor agonist isoproterenol are blunted in older, postmenopausal women compared to young, premenopausal women. We used venous occlusion plethysmography to measure forearm blood flow in young premenopausal (26 ± 1 years; n = 13) and postmenopausal (61 ± 2 years; n = 12) women. Forearm blood flow and mean arterial pressure were measured at baseline and during isoproterenol infusion at 1.0, 3.0, 6.0, and 12.0 ng/100 mL tissue/min. The two groups did not differ in body mass index or mean arterial pressure. Baseline forearm blood flow was similar between young and postmenopausal women (3.7 ± 0.5 vs. 2.9 ± 0.4 mL/100 mL tissue/min, respectively; P > 0.05). At the lowest dose of isoproterenol, forearm blood flow vasodilator responses were lower in postmenopausal women compared with young women (5.8 ± 0.4 vs. 7.4 ± 0.3 mL/100 mL tissue/min, respectively; P < 0.05). Thereafter, forearm blood flow remained similar between the groups for the remaining isoproterenol doses. In conclusion, β-adrenergic receptor-mediated forearm vasodilator responses are blunted in healthy, older postmenopausal women at lower but not higher doses of isoproterenol. This suggests that in aging women, β-adrenergic receptor-mediated vasodilator responses may be blunted at a moderate level of stimulation while maximum receptor responses are preserved.