In this review, we highlight that the relationship between muscle sympathetic nerve activity (MSNA) and mean arterial pressure is complex, differs by sex, and changes with age. In young men there is an inverse relationship between MSNA and cardiac output where high MSNA is compensated for by low cardiac output. This inverse relationship is not seen in older men. In young women sympathetic vasoconstriction is offset by β-adrenoreceptor mediated vasodilation, limiting the ability of young women to maintain blood pressure in response to orthostatic stress. However, β-mediated dilation in women is attenuated with age, leading to unopposed α-adrenergic vasoconstriction and a rise in the direct transduction of MSNA into increases in blood pressure. We propose that these changes with age and menopausal status are major contributing factors in the increased prevalence of hypertension in older women. In addition to aging, we highlight that changes in sex hormones in young women (across the menstrual cycle, with oral contraceptive use, or with pregnancy) influence MSNA and the transduction of MSNA into increases in blood pressure. It is likely that the β-adrenergic receptors and/or changes in baroreflex sensitivity play a large role in these sex differences and changes with alterations in sex hormones.
Keywords: autonomic function; blood pressure; neural control of blood pressure; sex differences.
Copyright © 2016 the American Physiological Society.