Johnson, Christopher P

In men, muscle sympathetic nerve activity (MSNA) is positively related to total peripheral resistance (TPR) and inversely related to cardiac output (CO). However, this relationship was not observed in young women. We aimed to investigate whether simultaneous β ‐adrenergic stimulation offsets this balance in young women. We measured MSNA (peroneal microneurography), arterial pressure (brachial line), CO (open‐circuit acetylene) and TPR before and after systemic β ‐blockade with propranolol in 6 young normotensive women (age; 24 ± 2 yrs, body mass index; 23 ± 1 kg/m 2 ). There was no difference in CO (5.7 ± 0.3 L vs. 5.3 ± 0.4 L), mean arterial pressure (MAP; 95 ± 3 mmHg vs. 95 ± 2 mmHg) before and after beta‐blockade. However, there was significant reduction in heart rate (HR; 61 ± 3 beats/min vs. 55 ± 2 beats/min, P <0.05). β ‐blockade caused an increase in TPR (17.4 ± 1.2 mmHg/ml/min vs. 18.5 ± 1.3 mmHg/ml/min; P =0.07) and MSNA (28 ± 3 bursts/100hb vs. 33 ± 3 bursts/100hb, P =0.08). Before β ‐blockade there was no relationship of MSNA to TPR, CO or MAP. Following β ‐blockade, there was a positive relationship between TPR and MSNA (r=0.60). However, there was no relationship of MSNA to cardiac output (r = −0.12). Interestingly, MAP became related to MSNA (r = 0.56). In summary, the β ‐adrenergic receptors appear to play a key role in the sympatho‐hemodynamic balance in young women. AHA 09POST2170087