Electroacupuncture at "Taichong"(LR3) improves baroreflex sensitivity and α2-adrenergic receptor activity in nucleus tractus solitarii of hypertensive rats

Abstract

To investigate the effect of electroacupuncture (EA) at "Taichong"(LR3) on blood pressure, sympathetic nerve activity, baroreflex sensitivity, and α 2-adrenergic receptor (α2AR) expression in nucleus tractus solitarii (NTS) in hypertensive rats, so as to reveal its mechanisms underlying improvement of hypertension. 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 α2AR positive neurons and α2AR protein expression in NTS were detected by using fluorescence immunohistochemistry and Western blot, respectively. The functions of α2AR within the NTS in modulating MBP and HR were verified by microinjection of its agonist (clonidine) and antagonist (yohimbine) separately. 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 α2AR positive neurons and α2AR 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 3rd and 4th 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 α2AR positive neurons and α2AR 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. 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 α2AR expression and functional activities.