Objective To investigate the effect of electroacupuncture(EA) at "Taichong"(LR3) on blood pressure

sympathetic nerve activity

baroreflex sensitivity

and α 2-adrenergic receptor(α2 AR) expression in nucleus tractus solitarii(NTS) in hypertensive rats

so as to reveal its mechanisms underlying improvement of hypertension. Methods Male Sprague Dawley rats were randomly divided into 4 groups: sham-operation

model

EA

and sham-EA(non-acupoint) groups

with 12 rats in each group. The hypertension model was established by occlusion of the right renal aorta(two-kidney-one clip method). Rats of the sham-operation group received the same surgery but without occlusion of the renal artery. EA(2 Hz/15 Hz

2 mA) was applied to bilateral LR3 for 30 min

once a day for 28 days

and sham EA was applied to the skin of the rat tail near the buttock on both sides. The mean arterial pressure(MAP) of the abdominal aorta and heart rate(HR) were recorded. The autonomic nerve function was assessed by using frequency domain analysis of heart rate variability(HRV)

and the baroreflex sensitivity detected by sequential method. Plasma norepinephrine(NE) level was measured by ELISA

and the α2 AR positive neurons and α2 AR protein expression in NTS were detected by using fluorescence immunohistochemistry and Western blot

respectively. The functions of α2 AR within the NTS in modulating MBP and HR were verified by microinjection of its agonist(clonidine) and antagonist(yohimbine) separately.Results Compared to the sham operation rats

the hypertension rats displayed significant increases in the MAP(P<0.01)

plasma norepinephrine content(P<0.01)

ratios of low frequency/total power(LF/TP) and low frequency/high frequency(LF/HF)(P<0.01)

and significant reduction in the overall gain

uplink sequence gain and downlink sequence gain of baroreflex(P<0.01)

the number α2 AR positive neurons and α2 AR protein expression level in NTS(P<0.01). The rats in the EA group(rather than in the sham-EA group) showed significant reduction in MAP at the 3 rd and 4 th week

plasma NE content

LF/TP and LF/HF(P<0.01)

and obvious increase in the overall gain

uplink sequence gain and downlink sequence gain of baroreflex(P<0.01)

and the number of α2 AR positive neurons and α2 AR protein expression in comparison(P<0.05) with those of the model group. Microinjection of clonidine into NTS induced an evident decrease in both MAP and HR in the model group relevant to the sham operation group(P<0.01)

while the MAP and HR changes of the EA(not sham EA) group were considerably bigger than those of the model group(P<0.05)

being similar to those of the sham-operation group(P>0.05)

which suggested an elimination of the BP-lowering effect of clonidine after EA. Conclusion EA at LR3 can reduce MBP

sympathetic activities

improve baroreflex sensitivity in renovascular hypertensive rats

which may be associated with its effects in up-regulating the decreased NTS α2 AR expression and functional activities.