Vasomotion In Resistance Vessel From Spontaneously Hypertensive Rat And Its Response To Antihypertensive Agents

Background and Objective: Vasomotion refers to the phenomenon of cyclical, rhythmical change of diameter and contractions with a certain frequency and amplitude in vascular tissue. Vasomotion occurs in small resistance vessels as well as in larger arteries both in vivo and in vitro either spontaneously or in response to pressure, stretch or application of vasoconstrictor agonists. Part of the studies have described a critical role for the voltage-dependent calcium channels, membrane potential, the IP3 receptor-mediated oscillatory change of intracellular calcium, phospholipase C and phospholipase A2 pathway on the vasomotion in different vessels. In pathological conditions of hypertension, such as in mesenteric artery from spontaneously hypertensive rat or from patients with pre-eclampsia, the amplitude of vasomotion in resistance artery increased significantly as compared with those of normal blood pressure. According to some studies, such phenomenon may be related to the increased gap junctions among vascular smooth muscle cells or the nitric oxide (NO) deficiency in endothelium, but the exact mechanism remains to be further defined. In addition, the significantly increased calcium influx in the vascular smooth muscle cells may also contribute to the enhanced vasomotion under the condition of hypertension.Recent studies found that the calcium influx in vascular smooth muscle cell can be mediated by transient receptor potential channels (TRPC) family, which can be divided into TRPC1, 2, 3, 4, 5, 6, 7 subtypes. In the hypertensive state, the expressions of TRPC3 channel in mononuclear cells and TRPC6 channel in artery smooth muscle cells as well as TRPC channel mediated calcium influx were increased significantly as compared with those of normal blood pressure. Studies have showed that the molecular composition of the store-operated calcium entry channels (SOCE), in which the emptying of intracellular calcium stores activates calcium influx, are TRPC1, TRPC3 and TRPC5. Now it is clear that the oscillatory change of intracellular calcium which result from the cyclical release and refilling of the intracellular calcium stores is associated with the formation of vasomotion, so it is possible that such a process can activate the TRPC channels rhythmically, which mediated calcium influx may be take part in the forming of enhanced vasomotion and recent study has showed that TRPC channels play an important role in the forming of calcium oscillations induced by ATP in human umbilical cord smooth muscle cells. This study will investigate the relationship between the enhanced vasomotion and the TRPC channels in resistance artery.At present, angiotensinⅡreceptor (type 1) blocker (ARB) and calcium channel blocker (CCB) are two widely used antihypertensive agents in clinic, not only can effectively lower the blood pressure but also can improve the vascular endothelial function and reverse the cardiovascular remodeling induced by hypertension. Studies have shown that long-term application of ARB on the SHR, the expression of TRPC3 was significantly reduced in aorta and the inhibition of TRPC3 channel by using RNA interference in vascular smooth muscle cells could significantly reduce the AngⅡ-mediated calcium influx. But, it is still largely unknown about the impact of ARB and CCB on the abnormal enhanced vasomotion in resistance artery from SHR. One of the important aims of the current study is to identify the impact of long-term application of candesartan, telmisartan and amlodipine on the abnormal vasomotion in resistance artery from SHR, and make a preliminary study on the possible mechanism.Methods:1. Animal grouping and treatment.In this study, three-month-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats weighing 250-260g were used. SHR were randomly divided into four groups: control group received distilled water (n=10), 5mg/kg/day telmisartan (n=10), 4mg/kg/day candesartan (n=10) and 10mg/kg/day amlodipine (n=10) by oral garage for 16 weeks. WKY were used as normotensive control group (n=10).2. Blood pressure measurement:Systolic blood pressure was measured monthly in conscious and restrained rats by the tail-cuff method.3. Vascular ring experiments: At the end of treatment, the magnitude of vasomotion in mesenteric artery from each group was measured and the effect of TRPC channel blocker on the vasomotion was also observed.4. Immunofluorescent staining:In order to show the expression of TRPC channel in mesenteric artery from SHR, the immunofluorescent staining was performed.5. Detection of protein expression of mesenteric artery from each group:Proteins of mesenteric artery from each group were extracted and western blotting was taken out to detect protein expression of TRPC1, TRPC3, TRPC4, TRPC5 and TRPC6.Results:1. Compared with WKY normotensive rat, the magnitude of vasomotion was significantly higher in mesenteric arteries from SHR (65.5±7.0% vs. 2.2±0.5%; each n=6, p<0.01);2. Compared with WKY normotensive rat, the expression of TRPC1, TRPC3 and TRPC5 channels were significantly higher in mesenteric arteries from SHR (TRPC1 expression for WKY 1.00±0.13 vs. 1.60±0.10 for SHR; p<0.01; TRPC3 expression for WKY 1.00±0.18 vs. 1.70±0.26 for SHR; p<0.05; TRPC5 expression for WKY 1.00±0.13 vs. 1.41±0.10 for SHR; p<0.05; each n=6);3. The blockers of TRPC channel can partially inhibit the markedly enhanced vasomotion in mesenteric artery from SHR and make the rhythm became derangement (gadolinium, from 107.3±10.7% to 63.1±10.6%; 2-APB, from 105.2±13.9% to 30.3±2.5%; SKF96365, from 109.9±15% to 23.5±9.6%; each n=6; p<0.05);4. Both candesartan, telmisartan and amlodipine can significantly reduce the blood pressure of SHR (placebo, 222±7mmHg; candesartan, 123±7mmHg; telmisartan 115±6mmHg; amlodipine, 122±5 mmHg; p<0.01; each n=10;), but only candesartan and telmisartan can significantly improve the abnormal enhanced vasomotion and amlodipine showed no effect on vasomotion (placebo control group, 66±7%; candesartan treated group, 14±3%; telmisartan treated group, 8±2%; amlodipine treated group, 57±7%; p<0.01, each n=10). At the same time, the expression of TRPC1, TRPC3 and TRPC5 were significantly reduced in mesenteric arteries from candesartan and telmisartan treated group compared to placebo-treated SHR as control group (p<0.05; n=5), while the expression of TRPC1, TRPC3 and TRPC5 showed no significantly change in mesenteric arteries from amlodipine treated group (p>0.05; n=5);Conclusions:1. The markedly increased expression of TRPC1, TRPC3 and TRPC5 in mesenteric artery from SHR may be related to the abnormal enhanced vasomotion;2. Candesartan, telmisartan and amlodipine can significantly reduce blood pressure in SHR, but only candesartan and telmisartan can reduce the expression of TRPC1, TRPC3 and TRPC5 in mesenteric artery from SHR and reduce the abnormal enhanced vasomotion;...