Study On The Biological Clock Mechanism About The Circadian Rhythm Of Blood Pressure Regulated By Valsartan In Spontaneously Hypertensive Rats

Circadian rhythm is one of the most common biological rhythms in the organic sphere.Many physiological and biochemical functions and behaviors of human beings showing rhythmic variations.Hypertension is one of the most common cardiovascular diseases.Nowadays,the circadian blood pressure rhythm pattern has been the reference standard for hypertension diagnosis and cardiovascular assessment.Angiotensin II(angiotensin II,Ang II)is closely related to the occurrence of hypertension,involved in the regulation of the circadian rhythm of blood pressure.Valsartan is a angiotensin receptor antagonist,which can selectively inhibit the AT1 receptor.Our previous clinical study had shown that with medication at different times,there was a significant effect of valsartan on the circadian rhythm of blood pressure in patients with non-dipper hypertension,especially for the asleep period,while the biological clock mechanism related to the regulation of the circadian rhythm of blood pressure is yet not clear.With the theoretical guidance of the core mechanism of biological clock circadian rhythm regulation theory,this experiment is set to explore how valsartan intervenes in abnormal circadian blood pressure rhythm and affects the diurnal variation expression of Per1,Per2 m RNA and protein,which is to clarify how the biological mechanisms ——Per1 and Per2 m RNA functions in the valsartan regulation of the circadian blood pressure rhythm from an overall perspective.The information this research obtained will provide a theoretical basis for hypertension chronotherapy and offer a new thinking mode for finding more ideal antihypertensive drugs.Objectives: To observe the regulation function of valsartan on the circadian blood pressure rhythm in spontaneously hypertensive rats and the effect of valsartan on blood pressure and the circadian blood pressure rhythm at different times,and to discuss the biological clock mechanismMethods: The ten-week-old male spontaneously hypertensive rats(SHR)and ten-week-old male Wistar-Kyoto rats(WKY)were fed in the biology laboratory for 2 weeks in which a 12 h light/12 h dark cycle was maintained.Referring to the circadian blood pressure rhythm in WKY rats as normal control group(asleep:awake ratio of SBP by 10 ~ 20%),the abnormal circadian blood pressure rhythm(asleep:awake ratio of SBP by <10%)in SHR was determined.Rats were randomly divided into three groups: SHR model group,valsartan 08:00 group and 20:00 group,and administrated with 30mg/kg valsartan by gavage,with continuous administration for 6 weeks.Each group was monitored with tail blood pressure for 24 hours before and after administration every 2 weeks by tail cuff method.After 6 weeks of administration,the animals in each group were killed every 4 hours from CT0 to CT24 under 10% chloral hydrate anesthesia for sample collection.The inspection indicators were as follows: plasma angiotensin II(Angiotensin II,Ang II),angiotensin converting enzyme(Angiotensin Converting,Enzyme,ACE),renin(Renin,REN)and aldosterone(Aldosterone,ALD),tested to observe the changes in 24 hours,and to analyze the circadian rhythm of targets by ELISA,to observe the degree of target organ injury in the heart and aorta respectively by HE and Masson staining,and to detect the expression of Per1,Per2 m RNA and protein in the hypothalamus and aorta in rats which could reflect the dynamic changes in 24 hours and the circadian rhythm,with Real-time PCR and Western blot respectively.Results:(1)During valsartan dosing,compared with model group,it was shown that in valsartan 08:00 group,systolic pressure,diastolic pressure and mean arterial pressure(P < 0.01)were decreased,blood pressure dipper value and the circadian blood pressure rhythm parameters amplitude were increased,median was debased and the phase shifted(P < 0.01),with the abnormal circadian blood pressure rhythm significantly improved(P < 0.01).The systolic pressure,diastolic pressure and mean arterial pressure were reduced(P < 0.01)in valsartan 20:00 group,while the blood pressure dipper value was not significantly increased.(2)After 6 weeks,compared with model group,the concentration of plasma Ang II in valsartan 08:00 group was increased in the asleep period,and reduced in the awake period.Circadian rhythm parameters amplitude was increased(P < 0.01),meanwhile in the overall period,the concentration of plasma renin was decreased,and the concentration of plasma angiotensin converting enzyme and aldosterone were increased(P < 0.01),changing the circadian rhythm of circulating RAAS system in valsartan 08:00 group.(3)After 6 weeks,compared with model group,the organ coefficients of target organs was decreased in valsartan 08:00 group(P < 0.01),and pathological damage of the heart and aorta was alleviated,but not in valsartan 20:00 group.(4)After 6 weeks,compared with model group,in valsartan 08:00 group,the expression of Per1 m RNA in hypothalamus was increased in the dark period as well as the Per2 m RNA in the asleep period(P < 0.05);(5)The expression of Per1,Per2 m RNA in aortic were decreased in the overall level,and circadian rhythm parameters median and amplitude were abated(P < 0.01);The expression of PER1 protein in aortic was raised in the dark period,as well as PER2 protein in the overall level(P < 0.01),changing the circadian rhythm expression of Per1,Per2 m RNA and protein in valsartan 08:00 group.Conclusions: Compared with dark phase administration,during light period administration,valsartan can effectively reduce SBP,BDP and MAP,improve the pathological damage degree of the heart and aorta and also improve the abnormal circadian blood pressure rhythm and reverse to the dipper circadian blood pressure rhythm pattern in spontaneously hypertensive rats,probably related to the circadian rhythm which affects the RAAS system,and then changes the diurnal rhythm expression of Per1,Per2 m RNA and protein in the heart and aorta.