Changes Of Muscle Sympathetic Nerve Activity In Spontaneously Hypertensive Rats At Different Weeks Of Ages

Objective This study was designed to Changes of muscle sympathetic nerve activity in spontaneously hypertensive rats at different weeks of ages,and to explore the role of sympathetic nervous system in the occurrence and development of the primary hypertension.Methods Male SHR(n=30)were randomly subjected to three groups by age:4-week-old group,12-week-old group,24-week-old group.Same sex and age matched Wistar-Kyoto Not motensive rat(WKY)served as control.Systolic blood pressure was measured using tail-cuff.Plasma concentration of NE,Ang Ⅱwas measured by enzyme-linked immunosorbent assay(ELISA).The level of MSNA was measured using by the microelectrode recording technique.The pearson rank correlation was applied to evaluate the ralationship of SBP to the level of plasma NE,MSNA.After the rats were sacrificed,heart and renal tissues were collected.Left ventricular mass index,renal mass index was measured.H-E histological section of heart and renal were made,and morphological characteristics were observed.Results 1 SBP,HR,CMI,KMI: Compared with age-matched WKY,SBP,CMI,KMI,of SHR in 12 w,24w group were significantly much higher(P<0.05),while it did not obviously change in 4w group(P>0.05).There was no difference among all groups on HR(P>0.05).2 The morphologic changes in heart,renal tissue: Hematoxylin-eosin staining results showed that myocardial hypertrophy,thickening coronary arterial wall was observed in left ventricle of the heart,and glomerulus hypertrophy,tubular revealed dilatation,thickening renal small arteriole wall was observed in renal tissue in SHR group of 12 w,24w.No pathological changes was observed in heart,renal tissue in 4w SHR group.There was no pathological changes in heart,renal tissue all WKY groups.3 The level of plasma NE: The level of plasma NE in SHR group of 24 w was not significantly different from that in SHR group of 12w(P>0.05),and the level of plasma NE in SHR group of 12 w was significantly higher than that in SHR group of 4w(P<0.05).The level of plasma NE in SHR group of 4w,12 w,24 w were significantly higher than that of age-matched WKY(P<0.05).4 The level of plasma AngⅡ: The level of plasma Ang in SHR group of 2Ⅱ 4w was not significantly different from that in SHR group of 12w(P>0.05),and the level of plasma AngⅡ in SHR group of 12 w was significantly higher than that in SHR group of 4w(P<0.05).The level of plasma Ang Ⅱin SHR group of 4w,12 w,24 w were significantly higher than that of age-matched WKY(P<0.05).5 The level of MSNA: With the increase of age,the level of MSNA in SHR groups increased gradually.The level of MSNA in SHR of 24 w group was the highest(55.38±5.16 mv.s),followed in SHR of 12 w group(41.7±3.92 mv.s),and was the lowest in SHR of 24 w group(32.7±2.84 mv.s).There was significant difference among three above groups respectively(P<0.05).The level of MSNA in SHR group of 4w,12 w,24 w were significantly higher than that of age-matched WKY(P<0.05).6 Correlation analysis showed that SBP was positively correlated with the level of MSNA(P<0.05).No relationship was found between SBP and the level of plasma NE or AngⅡ.Conclusions: 1 The SHR group of 12 w had shown the steady state of hypertension,and experienced target organ damage of hypertension including heart and kidney.The systolic blood pressure(SBP)in the SHR group of 24 w was significantly increased,and target organ damage of hypertension was further aggravated.2 The level of NE、Ang in the SHR groupⅡ were increased with aging from 4w to 12 w,and no longer changed at 24 w.3 The level of MSNA in the SHR group were increased with aging from 4w to 24 w.4 SBP of SHR was positively correlated with the level of MSNA but was not correlated with the level of plasma NE or AngⅡ,which had implied that the excessive activation of sympathetic nervous system might play a certain role in development and incidence of hypertension.