Mechanisms Underlying The Actions Of Electroacupuncture On Cardiovascular Function In Surgical Trauma Rats

Background:Surgical trauma is a stressor and may provoke changes in cardiovascular, respiratory and other physiological function, so that it can threaten the surgical safety and delay recovery in surgical patients. It is necessary to find stress releasing techniques which contribute to reduced complications, shortened length of convalescent recovery, and greatly improved operative outcomes. Acupuncture as a therapeutic intervention has been widely used in clinical medicine in humans and animal experiments, and it has shown enhancing effects on cardiac function in cardiovascular diseases. However, few experiments have been conducted to investigate the effect of acupuncture on cardiovascular function in surgical trauma stressed animals. The effects of acupuncture on cardiovascular diseases are related to the modulation on abnormal function of the autonomic nervous system. The hypothalamic paraventricular nucleus (PVN) and the rostral ventrolateral medulla (RVLM) are considered as key areas for modulating the function of the autonomic nervous system. Apelin is a new peptide that is the endogenous ligand for the APJ receptor, which can improve cardiac function. It is reported that Apelin can be produced in central nerves system, and APJ receptor can be expressed in the PVN. The present study was carried out to investigate the effects of electroacupuncture (EA) on cardiac function in surgical trauma stressed rats, and to answer the question whether the PVN and the RVLM participate in regulating the cardiac function when EA was applied on the surgical trauma stressed rats. Moreover, Apelin, a new neuromodulator, or amino acid neurotransmitters secreted from PVN or RVLM neurons may be involved in regulating cardiac function through humoral factors when Neiguan EA was applied. However, these possibilities require a great deal of investigation.Objectives:The present study was carried out to prepare the thoracotomy surgical trauma models and investigate the effect of EA on cardiac function in surgical trauma-stressed rats, and further study the mechanisms underlying the EA. The expression of c-Fos and electrophysiological characteristics of PVN and RVLM neurons in different groups were observed, so that the question whether the PVN and the RVLM participate in regulating the cardiac function when EA was applied on the surgical trauma stressed rats could be answered. The study investigated the expression of Apelin and APJ receptor in the PVN and the release of amino acids in the RVLM in order to further analyse the mechanism of neuromodulator or neurotransmitter action when EA was applied on the surgical trauma stressed rats.Methods:The rats were anesthetized, intubated and ventilated with a ventilator. The cavitas thoracis was exposed and lasted for60min. After surgery, the wounds were sutured and the ventilator was removed, then the thoracotomy surgical trauma models were prepared. Stainless steel needles were inserted into bilateral "Neiguan" points (PC6). The "Lieque (LU7)" acupoints were used as control. Animals were randomly divided into non-stressed group (Control), surgical trauma stressed group (Trauma), Neiguan EA applied on surgical trauma stressed group (Trauma+EA PC6) and Lieque EA applied on surgical trauma stressed group (Trauma+EA LU7). The effects of EA on cardiac function of thoracotomy trauma rats were investigated by detecting blood pressure and intraventricular pressure, as well as immunohistochemistry for c-Fos protein expression in each group. The intracellular recording techniques in PVN neurons of rat hypothalamic slices were used to observe the difference of electrophysiological characteristics of PVN neurons among Control, Trauma, and Trauma+EA PC6groups. Real time-polymerase chain reaction (Real time-PCR) methods were used to test the Apelin and APJR mRNA expression in the PVN in all groups. Micro-dialysis combining high performance liquid chromatography-fluorescence detection (HPLC-FD) method was exploited, by which we tested the amino acid transmitters in the RVLM in rats.Results:1. At60min after surgical trauma, almost all parameters of the cardiac function decreased significantly compared with those before thoracotomy trauma, including heart rate (HR)(P<0.01, n=7), mean arterial pressure (MAP)(P<0.05,n=7), maximal rate of intraventricular pressure rising (+dP/dtmax)(P<0.05, n=7) and declining (-dP/dtmax)(P＜0.05, n=7), and the total area of cardiac loop (Lo)(P＜0.05, n=7). At120min after surgical trauma, HR (P＜0.01, n=1) and-dP/dtmax (P<0.05, n=7) decreased significantly. After EA PC6treatment during the thoracotomy operation, the change of all parameters was not significant, except HR (P<0.05, n=6) at the time of60min after thoracotomy. Conversely, EA at the bilateral Lieque acupoints did not alter the induction of all parameters of the cardiac function. When Lieque EA was applied on trauma rats, HR (P<0.01, n=6), MAP(P<0.05,n=6),+dP/dtmax (P<0.01, n=6),-dP/dtmax (P<0.01, n=6), and L0(P<0.05,n=6) decreased significantly at the time of60min and120min after surgical trauma, and LVEDP (P<0.05,n=6) increased significantly at120min after surgical trauma.The rate of change in HR, MAP, LVEDP,+dP/dtmax (P＜0.05),-dP/dtmax and Lo between preoperative time and postoperative time in Trauma+EA PC6group (n=6) was lower than that in Trauma group (n=7). No significant deviation in the rate of change in HR, MAP, LVEDP,-dP/dtmax and L0was observed between Trauma+EA LU7group (n=6) and Trauma group, even the the rate of+dP/dtmax change increased significantliy compared with the Trauma group (P<0.05).2. At60min after operation, a significant increase in the expression of c-Fos in the PVN of hypothalamus and the RVLM (P<0.05) was found in the trauma rats, compared with that in the control animals. When Neiguan EA was applied on trauma rats, the number of Fos-IR neurons of the PVN and the RVLM (P<0.05) dropped, respectively, compared with that of the Trauma group. On the contrary, EA at Lieque did not significantly decrease c-Fos expression in the PVN and the RVLM of trauma rats, and Fos-IR neurons in the PVN increased significantly (P<0.01) compared with Control group. At120min after operation, the number of Fos-IR neurons of the PVN and the RVLM was higher in the Trauma rats than that in the Control rats, and the number of Fos-IR neurons of the PVN and the RVLM decreased when Neiguan EA was applied, compared with that in the Trauma animals.3. The rheobase in Trauma group decreased significantly (P＜0.01) and membrane resistance increased significantly (P<0.01), compared with that in Control group. Significant change could not be observed in the other parameters in Trauma group compared to Control group. In Trauma+EA PC6group, the rheobase increased, while membrane resistance and Max L. slope (P<0.05) decreased significantly, compared with that in Trauma group. The excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) in PVN neurons were elicited by electrical stimulation near the fornix. The excitatory postsynaptic potentials (EPSPs) were elicited in69%of tested PVN neurons, and inhibitory postsynaptic potentials (IPSPs) in6%of tested PVN neurons by electrical stimulation near the fornix in Control group (n=16). However, in Trauma group, the EPSPs could be elicited only in10%of10tested PVN neurons by electrical stimulation near the fornix and the inductivity of the postsynaptic potentials decreased significantly (P<0.01). In Trauma+EA PC6group, electrical stimulation near the fornix evoked EPSPs in50%of8PVN neurons. The inductivity of the postsynaptic potentials increased.4. Realtime-PCR showed Apelin mRNA and APJ receptor mRNA expression in the PVN was lower in Trauma group, compared with that in Control group, while that increased in the PVN when Neiguan EA was applied in surgical trauma rats.5. In Trauma group, In the dialysate from the RVLM at the postoperative120min, inhibitory amino acid (IAA) taurine (Tau) increased compared with that in Contol group (P<0.05, n=5). EA colud decreased Tau in Trauma+EA PC6group. At the postoperative60min, Tau was higher than that in Control group, and it was lower than that in Trauma group when EA was applied. However, the release of the excitatory amino acid (EAA) glutamate (Glu) had no significant change in all groups at the postoperative60min and120min.Conclusions:The thoracotomy surgical trauma models could be successfully prepared in rats. Surgical trauma stress dramatically attenuated cardiac function. Neiguan EA can improve cardiac function in surgical trauma stressed rats in a point-specificity way. These results indicate that the neurons of the PVN and the RVLM may be involved in the regulation of cardiac function when EA was applied on surgical trauma stressed rats. We supposed that the reduction of Apelin and APJR mRNA expression induced by surgical trauma can attenuate their protection on heart, and then led to the decrease in cardiac function. Furthermore, the decrease of cardiovascular function caused by trauma may be related to increasing of taurine in the RVLM. The promoting of Apelin and APJR expression in the PVN and the reduction of Tau in the RVLM could exert the protection on heart after Neiguan EA.