Blood pressure changes during orthostatic stress: evidence of gender differences in neuroeffector distribution

BACKGROUND: Research has demonstrated that exogenous adrenergic agonists produce dose-related vasoconstriction in men but not women. This suggests that the distribution of adrenergic receptor sites differ with gender. Women may have a higher density of receptor sites in the arterioles (fast acting with low gain) while men may have higher density in the larger vessels (slow acting with high gain). METHODS: To partially test this hypothesis, the time course in beat-to-beat responses in systolic and diastolic BP, and heart rate was compared between six men and six women during the transition from a supine to an upright posture and during prolonged standing. RESULTS: The transient change in systolic and diastolic BP was very rapid in women, but completed within 15 to 30 s after assuming an upright position. Men increased BP at a much slower rate, but continued to produce higher BPs over the complete testing session (up to 15 min). The rate of change for men (15 mm Hg systolic and 10 mm Hg diastolic) was approximately half that for women (30 mm Hg systolic and 15 mm Hg diastolic) during the first 30 s of upright posture. However, after 60 s of standing, absolute change in systolic BP for the men exceeded that of the women by approximately 5 mm Hg for both systolic and diastolic BP. While men's heart rate remained relatively constant during standing, women compensated for the lower change in BP by a continual increase in heart rate throughout the duration of the test. Although both men and women demonstrated increases in norepinephrine at 5 and 15 min during standing, no difference between genders was observed. Similarly, there were no differences in dominant periodicity of heart rate during standing, although women demonstrated slightly higher beat-to-beat variation (RMS) than men. CONCLUSION: The results support the hypothesis of distributional differences in neuroeffector responses between men and women and have implications for how men and women respond to orthostatic stress across a variety of environmental conditions.