Forearm vasodilatation to a β₂ -adrenergic receptor agonist in premenopausal and postmenopausal women

What is the central question of this study? What is the role of β₂ -adrenergic receptor (β₂ AR) vasodilatation in older postmenopausal women as compared to premenopausal women and the role of nitric oxide (NO) in β₂ AR-mediated vasodilatation in both groups of women? What is the main finding and its importance? β₂ AR responsiveness is blunted in postmenopausal women compared to young premenopausal women. Additionally, NO may contribute to β₂ AR-mediated vasodilatation in young premenopausal women.

β₂ -Adrenergic receptor (β₂ AR)-mediated vasodilatation, which is partially dependent on nitric oxide (NO) formation, is blunted in men at risk for developing hypertension. However, the role of β₂ AR vasodilatation in hypertension pathophysiology in ageing postmenopausal women is unclear. Therefore, the goals of this study were to determine if forearm vasodilatation to the selective β₂ AR agonist terbutaline is blunted in older postmenopausal women (59 ± 4 years) compared to young premenopausal women (27 ± 3 years) and to assess NO contribution to β₂ AR-mediated vasodilatation in both groups of women. Forearm blood flow (FBF) and forearm vascular conductance (FVC) were measured using venous occlusion plethysmography at baseline and during intra-arterial infusions of terbutaline at 0.1-2.0 µg (100 ml tissue)^-1  min^-1 with and without the NO synthase inhibitor l-N^G -monomethylarginine (l-NMMA). Mean arterial pressure was significantly greater in postmenopausal women than in young women at baseline (P = 0.01). Baseline FBF and FVC did not differ between young and postmenopausal women (P > 0.05) and rose significantly within each group during terbutaline infusion (P < 0.05). There were significant group × dose interactions for FBF (P = 0.01) and FVC (P = 0.001), indicating vasodilator responses were lower in postmenopausal women. In young women, FVC response to the highest dose of terbutaline tended to be lower with l-NMMA co-infusion vs. without l-NMMA (P = 0.05). There were no significant decreases in FBF or FVC responses to terbutaline in postmenopausal women with l-NMMA co-infusion (P > 0.05 for all). These data suggest that β₂ AR responsiveness is blunted in postmenopausal women compared to young premenopausal women, and that NO may contribute to β₂ AR-mediated vasodilatation in young premenopausal women.