Abstract
Acupuncture lowers blood pressure (BP) in hypertension, but mechanisms underlying its action are unclear. To simulate clinical studies, we performed electroacupuncture (EA) in unanesthetized rats with cold-induced hypertension (CIH) induced by six weeks of cold exposure (6 °C). EA (0.1 – 0.4 mA, 2 Hz) was applied at ST36-37 acupoints overlying the deep peroneal nerve for 30 min twice weekly for five weeks while sham-EA was conducted with the same procedures as EA except for no electrical stimulation. Elevated BP was reduced after six sessions of EA treatment and remained low 72 hrs after EA in 18 CIH rats, but not in sham-EA (n = 12) and untreated (n = 6) CIH ones. The mRNA level of preproenkephalin in the rostral ventrolateral medulla (rVLM) 72 hr after EA was increased (n = 9), compared to the sham-EA (n = 6), untreated CIH rats (n = 6) and normotensive control animals (n = 6). Microinjection of ICI 174,864, a δ-opioid receptor antagonist, into the rVLM of EA-treated CIH rats partially reversed EA’s effect on elevated BP (n = 4). Stimulation of rVLM of CIH rats treated with sham-EA using a δ-opioid agonist, DADLE, decreased BP (n = 6). These data suggest that increased enkephalin in the rVLM induced by repetitive EA contributes to BP lowering action of EA.
Highlights
We have shown in previous studies of patients with mild to moderate hypertension that electroacupuncture (EA) applied once weekly over an eight-week course of therapy lowers peak systolic blood pressures (SBP) by 10 – 12 mmHg as measured by 24 hr ambulatory monitoring[7]
Despite strong evidence showing that acupuncture influences short-term hypertensive reflexes, it is uncertain if opioids in the rostral ventrolateral medulla (rVLM) participate in the BP lowering actions of repetitive EA in chronic hypertension
EA reduced both the elevated SBP and DBP after six sessions; the BPs remained low throughout the period of treatment relative to the sham treated group
Summary
We have shown in previous studies of patients with mild to moderate hypertension that electroacupuncture (EA) applied once weekly over an eight-week course of therapy lowers peak systolic blood pressures (SBP) by 10 – 12 mmHg as measured by 24 hr ambulatory monitoring[7]. This response appears to persist for an additional four weeks after EA is terminated. To simulate clinically relevant hypertension due in part to sympathoexcitation, the conscious CIH rat model was used in the present study to investigate the effect of repeated EA on BP and the mechanisms underlying EA’s action in a relevant brain stem region, the rVLM. We hypothesized that repetitive EA lowers CIH in conscious animals through the opioid system in the rVLM
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