The Changes Of The Density Of Cardiac Sympathetic Nerves And Norepinephrine Transporter Expression In Aged Rats And Its Possibly Infactors

Objective: To observe the relationship between age-related changes of the density of cardiac sympathetic nerves and norepinephrine transporter(NET) expression in rat myocardia, and discuss its physiological roles.Method: 3- (n=5), 10- (n=5) and 16-month-old (n=5), male Sprague-Dawley(SD) rats were used in this study. (1) To investigat the changes of hearts'function, cardiac sympathetic nerves density and norepinephrine transporter expression ,We use some methods as follows: (1) study function of left ventriclular by echocardiogram,determine ventricular wall thick,left ventricular end-diastolic diameter (LVDd),left ventricular end-diastolic diameter (LVDs),ejection fraction(EF),fractional shortening(FS)and so on; (2) examine hemodynamic parameters: mean blood pressure (MBP) , left ventriclular systolic pressure (LVSP) , left ventricular end-diastolic pressure (LVEDP), max velocity rate changes of left intraventricular pressure (±dp/dtmax) and ventricular mass index (left ventricular mass index , LVMI; right ventricular mass index , RVMI), and observed structure changes of hearts with different ages;(3)Use Picrosirius-polarization staining to detect collagen volume fraction(CVF) in left ventricular myocardium of all three groups: slice up, bake, dewax to water in order, then dip in hematoxylin and dip in picrosirius red at last. All stain results were observed under Polarization microscopy , analysised with software Image Pro Plus 6.0.(4) immunohistochemical stain of tyrosine hydroxylase(TH) and NET: left ventriclulars of three groups were removed and fixed in 4% paraformaldehyde solution .Then routine paraffin sections were made and stained with immunohistochemical method. All stain results were observed under microscope,analysised with software Image Pro Plus 6.0 and counted positive points.Results: Comparison of three age groups: (1) echocardiogram:during the process of aging,ventricular walls became thicker, ejection fraction (EF) and left ventricular fraction shortening(FS) had no various alteration.( 2 ) hemodynamic parameters: Comparing with 3-month-old group, LV-dp/dtmax of 10-month-old group and 16-month-old group decreased obviously(P<0.05),but there was no difference between 10-month-old group and 16-month-old group(P>0.05).There were also no difference in MBP,LVSP,LVEDP,LV+dp/dtmax among groups(P>0.05). (3)changes of heart structure: Heart and left ventricular chamber had a age-related increase; under light microscope, cardiac muscle fibers became thicker with age,aranged in order; There were no significant different in LVMI and RVMI among three groups(P>0.05).(4) Picrosirius-polarization staining:CVF of 3-month-old group and 10-month-old group declined evidencely incomprison with 16-month-old group(P<0.05),but there was no difference between 3-month-old group and 10-month-old group(P>0.05). (5) immunohistochemical stain of TH and NET: positive points of NET in myocardium of 10-month-old group and 16-month-old group declined markedly in comparison with those in 3-month-old group(P<0.05);comparing with 10-month-old group, NET protain descended distinctly,too(P<0.05). Positive points of TH in myocardium of 10-month-old group and 16-month-old group declined notablely in comparison with 3-month-old group, and there were differences among all three groups(P<0.05). The expression levels of NET and TH in the myocardia of 16-month-old rats were markedly reduced by 25.4% and 51.2% respectively, in comparison with those in 3-month-old rats.Conclution: In the process of aging, 1. the density of cardiac sympathetic nerves and NET protain all decreased, and maybe there were some relations between the two things. 2.The age-dependent reduction of NET activity may have relation to the descend of NET protain content. 3.Left ventricular diastolic function reduced, and this may had something with the developed activity of sympathetic nerves which was due to dropped activity of NET.