Blood pressure rhythm and endocrine functions in normotensive women on oral contraceptives

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Abstract
Twenty-four hour blood pressure profiles were determined by non-invasive ambulatory blood pressure measurements in young normotensive women during the follicular and luteal phases of the menstrual cycle. Forty women participated, 20 of whom were on oral contraceptives (ethinyl-ethylestradiol 0.03 mg + levonorgestrel 0.15 mg) and 20 of whom were age- and weight-matched control individuals not on oral contraceptives. Data on systolic and diastolic blood pressure and heart rate were analyzed in each case by linear and rhythm analysis. Urine was collected day and night on each occasion on which ambulatory blood pressure measurements were recorded.Daytime, night-time, and 24 h mean systolic and diastolic blood pressure and heart rate did not depend on the cycle phase. The nocturnal fall in blood pressure was preserved in both groups and during both phases. Rhythm analysis by partial Fourier series showed that, of 240 individual 24 h blood pressure profiles, only 12 (5%) did not exhibit a significant circadian rhythm. Linear and rhythm analyses revealed that during both phases of the menstrual cycle systolic and diastolic blood pressure were significantly higher throughout the 24 h, especially during the night, in women taking oral contraceptives. During both phases of the menstrual cycle urinary aldosterone excretion was significantly higher in women taking oral contraceptives. This increase could contribute to the night-time blood pressure elevations caused by oral contraceptives. The results suggest a modulating influence of sex steroids on the circadian blood pressure profile even in normotensive healthy volunteers.Noninvasive ambulatory blood pressure monitoring has shown that blood pressure exhibits a pronounced circadian variation in both normotensive volunteers and patients with essential hypertension, with a daytime peak and a nocturnal fall. To investigate the effect of oral contraceptives (OCs) on the 24-hour blood pressure profile during the follicular and luteal phases of the menstrual cycle, a case-control study was conducted involving 20 users of OCs (0.03 mg ethinyl estradiol and 0.15 mg levonorgestrel) and 20 age- and weight-matched healthy controls. Linear and rhythm analyses revealed that both systolic blood pressure (SBP) and diastolic blood pressure (DBP) were significantly higher in OC users than in controls throughout the 24-hour observation period. The 24-hour, daytime, and nighttime means of SBP and DBP were not dependent on menstrual cycle phase. In both groups, peak SBP values occurred around 15-17 hours, trough values at 4-5 hours at night, and maximum slopes between 8-10 in the morning. Of the 240 individual 24-hour blood pressure profiles analyzed, only 12 (5%) did not exhibit a significant circadian rhythm. Finally, urinary aldosterone excretion was significantly higher among OC users in both phases of the menstrual cycle.

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