| Hypertension, which can easily be complicated by some serious complications, such as coronary heart disease, heart failure, stroke and renal failure etc, is a very common and harmful disease with a high incidence. And the psychosocial stress of humans, which is gradually increasing as the pace of life speeding up in modern society, is an important risk factor for this disease. Moreover, the stress-induced hypertension becomes an increasingly big proportion in hypertension incidence. Thus, the investigation of pathogenesis of stress-induced hypertension is becoming really important.APJ receptor, the putative receptor protein related to the angiotensin II type1receptor (AT1), is a G-protein coupled receptor, while Apelin acts as its endogenous ligand. The Apelin/APJ system has much relevance in regulation of cardiovascular system. It has been reported that there is strong association between APJ receptor genetic polymorphisms and essential hypertension in human and that enhanced function of Apelin/APJ system contributes to hypertension in the rostral ventrolateral medulla (rVLM) in spontaneously hypertensive rats. It is unknown whether this system is also involved in the pathogenesis of stress-induced hypertension.Acupuncture, used as an important treatment for a long time in Chinese traditional medicine, is widely used to treat many diseases, while hypertension is one of these diseases, to which acupuncture has its definite therapeutic effects with little side effects. It has been reported that acupuncture can elicit hypotensive effects via regulating some signal pathway in the rostral ventrolateral medulla in hypertensive rats, but it is obscure if the Apelin/APJ system, which participates in the pathogenesis of hypertension, is also a target for acupuncture regulating in the rVLM in rats.The hypothesis of the present study is that the activity of the medullary Apelin/APJ system may increased by physical and mental stress, and in turn elicit the incidence of hypertension, while the electroacupuncture treatment can induce hypotensive effects by inhibiting the activity of the Apelin/APJ system.In this study, healthy male SD rats weighing250-280g were divided randomly into 4groups, control rats, stress-induced hypertension rats (SIHR), stress-induced hypertension rats with electroacupuncture treatment (SIHR+EA) and stress-induced hypertension rats with sham electroacupuncture treatment (SIHR+SEA). The control rats were given regular breeding. While the SIHR were given stress using electric foot-shocks combined with noises for continuous14days. And in the SIHR+EA and SIHR+SEA groups, individuals with over20mmHg elevation in blood pressure after stress were treated with electroacupuncture, stimulating the acupoint of Zusanli, and sham electroacupuncture, stimulating non-point tissue, respectively during the10-14days of stress.The techniques used in this study include cerebral perfusion fixation, frozen slicing, immunohistochemistry, central microinjection and neutral red staining etc.The tail artery blood pressure of rats was measured using a tail-cuff monitor during the preparation process of hypertensive animal models, and the results showed that the blood pressure of SIHR, SIHR+EA and SIHR+SEA began to increase and had a significant difference (p<0.01) when compared to that of control rats since the third day of the stress stage; While from the treatment of electroacupuncture on, the blood pressure of SIHR+EA started to decrease and had a significant difference (p<0.01) when compared to that of SIHR and SIHR+SEA since the third day of electroacupuncture stage; On the fifth day during electroacupuncture stage, also the last day of stress stage, despite the increased tendency of blood pressure of individuals in SIHR+EA group was observed, there was no statistical difference (p=0.92) on blood pressure as compared to that of individuals in Control group; Also, there was no significant difference (p>0.05) on the blood pressure between the groups of SIHR and SIHR+SEA during the whole process.When the preparation of hypertensive animal models was completed, femoral artery systolic blood pressure of rats in all groups was measured under anesthetized condition. And the results showed that the femoral artery systolic blood pressure of SIHR (160.58±3.32mmHg) was significantly high (p<0.01) compared to that of control rats (116.00±2.00mmHg); the femoral artery systolic blood pressure of SIHR+EA (119.69±2.84mmHg) was markedly decreased (p<0.01) compared to that of SIHR; while the femoral artery systolic blood pressure of SIHR+SEA (159.92±3.01mmHg) had no significant difference (p=0.99) with that of SIHR. These results demonstrate that the hypertensive animal models are reliable, the hypotensive effects of electroacupuncture are definite, and that the sham electroacupuncture has no hypotensive effects. Thus, animal models in all groups can be used for subsequent study s.The Apelin and APJ receptor expression were detected with immunohistochemistry, and the results revealed that the expression of Apelin (number of Apelin immunoreactive neurons and relative optical density) was significantly increased (p<0.01) in the rVLM of SIHR compared with that of control rats; the expression of Apelin in the rVLM of SIHR+EA was remarkablly decreased (p<0.01) when compared with that of SIHR, but had no significant difference (p=0.82, p=0.89) when compared with that of control rats; the expression of Apelin in the rVLM of SIHR+SEA had no significant difference (p=0.84, p=0.79) as compared with that of SIHR. The results also revealed that the expression of APJ receptor (number of APJ immunoreactive cells and relative optical density) in the rVLM was similar (p=0.92, p=0.96) among all (4) groups. These results suggest that the Apelin/APJ system is probably enhanced in the rVLM of rats in SIHR group, and that electroacupuncture may elicit hypotensive effects by inhibiting the enhanced Apelin/APJ system in the rVLM of individuals in SIHR+EA group.Using central microinjection, the hypertensive effects of medullary Apelin in each group were compared, and the total activity of APJ receptor in the rVLM of each group rats were also compared though indirectly. The results indicate that medullary Apelin could induce significantly greater elevation on blood pressure in SIHR compared to that of control rats; while in SIHR+EA, the elevation of blood pressure was significantly lower when compared with that of SIHR, but had no significant difference when compared with that of control rats; the elevation of blood pressure in SIHR+SEA also had no significant difference as compared with that in SIHR. These results suggest that the total activity of APJ receptor is increased in the rVLM of SIHR; while in the SIHR+EA, electroacupuncture treatment can decrease the increased APJ receptor activity; but in the SIHR+SEA, sham electroacupuncture treatment had no such effects. Coupled with the immunohistochemistry results and hypertensive effect of Apelin in the rVLM, the results suggest that the activity of Apelin/APJ system is enhanced in the rVLM of rats in SIHR group, and the enhanced Apelin/APJ system contribute to the pathogenesis of SIHR.In the SIHR, microinjection of APJ receptor antagonist (Apelin-13, pGlu1, Ala13) into the rVLM did not elicit significant hypotensive effects. However, pretreatment of microinjection of APJ receptor antagonist into the rVLM2minutes before the microinjection of Apelin, can significantly attenuate the hypertensive effects of Apelin in the rVLM.Taken together, the conclusions of the present study are that the enhanced Apelin/APJ system in the rVLM of SIHR contributes to the pathogenesis of hypertension though this mechanism may not be the major one; and that the electroacupuncture treatment elicits hypotensive effects probably via inhibiting the enhanced Apelin/APJ system in the rVLM of SIHR+EA though this pathway may not be the most important one. |
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