The Effects of Gender on Adrenergic Receptor Responsiveness

Abstract

This study was conducted to determine whether gender differences exist in adrenergic receptor sensitivity and baroreflex response. Adrenergic receptor sensitivity was assessed by administering sequentially increasing intravenous doses of phenylephrine and isoproterenol. Baroreflex sensitivity was determined from the slope of pulse intervals plotted against phenylephrine-induced rise in systolic blood pressure (SBP). Drug-induced changes in heart rate, blood pressure, and brachial artery diameter were measured and statistically compared. Women required a lower infusion rate of phenylephrine to increase SBP by 20 mmHg from baseline. There were no statistically significant gender-related differences in baroreflex sensitivity. The dose of isoproterenol needed to increase heart rate by 25 beats per minute from baseline also did not differ significantly between groups. Percent changes from baseline in brachial artery diameters in response to phenylephrine also were similar between groups. These data suggest that women may have greater alpha-adrenergic receptor sensitivity than men, whereas beta1-adrenergic receptor sensitivity is similar between genders. A trend toward a greater baroreflex sensitivity in men than in women was also observed. This study also provides evidence for a possible relationship between adrenergic receptor sensitivity and baroreflex sensitivity.

Women Have Lower Tonic Autonomic Support of Arterial Blood Pressure and Less Effective Baroreflex Buffering Than Men

“…Moreover, women often demonstrate less effective BP regulation than men during acute challenges (eg, orthostatic stress) and in response to vasoactive drugs. 1,2,4,6,[11][12][13][14] The responsible mechanisms have not been identified, but the results of the present study indicate that a reduced ability for BRB of acute changes in BP may play a central role in the less effective short-term BP control observed in women.…”

“…The present results represent the first direct measurements of systemic ␣-adrenergic vascular responsiveness in men and women and correct previous findings of gender-related differences in responsiveness based on BP responses to systemic infusions of ␣-adrenergic agonists with intact baroreflexes. 13 We have shown that circulating levels of vasopressin increase in response to the decrease in BP produced by GB. 7,15,19 The vasoconstrictor effects of vasopressin can counteract the reductions in BP during GB and thus lead to an underestimation of tonic ANS support of BP.…”

“…13 We previously demonstrated that BRB is strongly and inversely related to this pressor response to phenylephrine in healthy men and patients with ANS-cardiovascular disorders. 9,10 In the present study, we found a similarly strong, inverse curvilinear relation among the pooled male and female subjects ( Figure 3).…”

“…The ability of baroreflexes to "buffer" acute changes in BP under such conditions (ie, baroreflex buffering [BRB]) is reduced in certain physiological 9 and disease 10 states associated with impaired short-term BP regulation and/or altered responsiveness to vasoactive medications. In light of previous reports of less effective short-term regulation of BP in women than in men, 1,2,6,[11][12][13][14] we also hypothesized that premenopausal women have lower BRB of BP than men of similar age.…”

Endogenously and exogenously increased noradrenaline exerts sex-different responses in humans

“…Again, these results are in accordance with previous studies. 8,9 These functional experiments also demonstrate that the vascular response caused by elevated luminal concentrations of noradrenaline is different from that released neuronally. 10 An increase in systemic plasma concentrations of noradrenaline by exogenous infusion by approximately nine-fold as compared to tyramine did only translate into a three-fold increased blood pressure response.…”