Low-dose Aspirin Inhibits Cardiac Sympathetic Activation and Vagal Withdrawal Response to Morning Rising

Aspirin is known to interfere with platelet function and can protect individuals at risk of sudden death. However, this property of aspirin is less defined for cardiac autonomic activity. We assessed pulse rate variability by spectral analysis and measured plasma eicosanoid levels before and after administration of 81-mg aspirin to 12 healthy subjects over a 60-degree head-up tilt test in the morning. In upright posture, low-dose aspirin decreased both the normalized unit value of low-frequency (normalized LF) power (mean ± SD, 82.5 ± 4.5 vs. 77.5 ± 6.5 nu, P = 0.01) and LF/HF ratio (6.0 ± 2.1 vs. 4.7 ± 2.7, P = 0.02) and augmented the normalized unit value of high-frequency power (15.0 ± 4.4 vs. 19.8 ± 6.4 nu, P = 0.004). It simultaneously upregulated plasma 6-keto-PGF1α level (13.4 ± 6.8 vs. 19.7 ± 12.8 pg/mL, P = 0.04) and inhibited plasma thromboxane B2 (TXB2) level (11.6 ± 7.3 vs. 6.3 ± 4.2 pg/mL, P = 0.003). In the upright posture, both before and after aspirin, there was a significant direct correlation between plasma TXB2 levels and the normalized LF power (r = 0.42, P = 0.04) as well as between the plasma TXB2/6-keto-PGF1α ratio and the normalized LF power (r = 0.50, P = 0.01). Administration of low-dose aspirin in healthy people inhibits cardiac sympathetic activation and vagal withdrawal response to morning rising through an alternation of the TXA2/PGI2 balance.