Doxazosin suppresses the morning increase in blood pressure and sympathetic nervous activity in patients with essential hypertension.

To investigate the effects of doxazosin on blood pressure and sympathetic nervous activity, we analyzed the circadian variation of blood pressure and the power spectrum of R-R intervals using an ambulatory multibiomedical monitoring system (TM2425) in 10 untreated outpatients with essential hypertension. After a 2-wk placebo period (P-period), we administered 1 to 4 mg of doxazosin mesilate to the patients for 2 to 6 wk (T-period). We measured systolic and diastolic blood pressure (SBP, DBP), heart rate, R-R intervals, posture, and activity with the use of TM2425. Power spectral analysis of R-R intervals was used to calculate the ratio of low to high frequency components (LF/HF). The values were compared between the P-period and T-period. Although daytime blood pressure significantly decreased during the T-period (SBP, 148.1 +/- 5.9 vs. 130.3 +/- 4.4 mmHg; DBP, 92.3 +/- 3.2 vs. 83.6 +/- 2.6 mmHg, p < 0.01), nighttime DBP did not. The LF/HF of R-R intervals in the daytime (5.8 +/- 2.0 vs. 4.9 +/- 1.2, p < 0.01) and the morning rise in blood pressure also decreased significantly (SBP, 17.5 +/- 9.4 vs. 12.1 +/- 6.5 mmHg; DBP, 12.5 +/- 6.5 vs. 8.3 +/- 5.3 mmHg, p < 0.05). We conclude that doxazosin may suppress the morning rise in blood pressure in association with a decrease in sympathetic nervous activity.