Effects Of Fatty Acids And Isoproterenol On Myocardial Contractility In Hypertensive Rats

Fatty acid metabolism is predominat in cardiomyocyte ATP production in healthy heart.Therefore,fatty acid is an important prerequisite for maintaining regular contraction of myocardial cells.Fatty acids are also the precursors for cardiac arrhythmias in diseased hearts.It has been reported that fatty acid metabolism in the myocardium of hypertensive rats is significantly reduced,and fatty acids can be important causes of ventricular arrhythmias,sudden cardiac death,and heart failure.In addition,hypertension and hyperlipidemia are accompanied by systemic and local inflammatory reactions.So far,the effect of fatty acids on the contraction of normal and hypertensive myocardial cells and the response to inflammatory factors remain to be studied.Therefore,this experiment observed the effects of fatty acid on LV myocyte contraction using sham and angiotensin II(Ang II)-induced hypertensive rat left ventricular(LV)myocytes.Furthermore,we also observed ?-adrenergic receptor stimulation with isoprenaline(ISO)and inflammatory cytokine(IL-6)-regulation of the effects.NOS protein expression in response to Ang II was examined as in indicator of inflammation.Objectives:1.Observe the effects of saturated fatty acid(palmitic acid,PA)on the contraction of normal and hypertensive LV mryocytes;2.Compare the effects of PA and PA+ISO on contraction of LV myocytes in two groups;3.To analyze in detail the characteristics of contraction of hypertensive LV cardiomyocytes under the action of PA and PA+ISO;4.Observe the effects of IL-6 on PA and PA+ISO regulation of normal and hypertensive LV myocyte contraction;5.Detect iNOS protein expression in response to Ang II,PA and IL-6 in H9C2 cell lines.Methods:1.Ang II containing osmotic minipump was inserted subcutaneously in rats to establish hypertensive model.Similar operational procedures were undertaken in sham rats without implanting osmotic pump and Ang II.2.LV myocytes were isolated using Langendorff perfusion system,perfusing normal tyrode solution(NT)containing collagenase II.3.Using IonOptix system to measure the changes in sarcomere length of LV myocyte(contraction),compare the effect of NT,NT + PA and NT + PA + ISO on myocyte contraction.4.Study whether IL-6 affects LV myocyte contraction in NT,NT+PA,and NT+PA+ISO.5.Observe iNOS protein expression in H9C2 cell line in response to AngII,PA,AngII+PA and AngII+PA+ISO with and without IL-6,respectively.Results:1.Field stimulation of cardiomyocytes at 2Hz and correspondingchanges in sarcomere length are analyzed as the degree of myocyte contractoiPA increased LV myocyte sarcomere length(contraction)in sham rats(P<0.001,n=14);ISO+PA further enhranced LV myocyte contraction(P<0.001,n=14).2.The contraction of LV myocyte in hypertensive rats showed different responses to PA treatment:some were enhanced(P<0.001,n=12),and some were not enhanced or slightly reduced(P=0.001,n=6).However,ISO+PA further increased the degree of LV myocyte contraction in both groups and LV myocyte contraction was similar between the two groups(n=14,n=18).3.Irregular contractions occur with PA + ISO and the frequency was significantly higher in hypertension than that in sham(3 times more in hypertension).4.IL-6 does not alter the effects of PA and PA+ISO on LV myocyte contraction in sham;however,IL-6 has a tendency of reducing PA+ISO-induced abnormal contractions.5.Western blot results showed that Angll increased the expression of iNOS protein in H9C2 cells(P<0.05,n= 11);addition of ISO and PA did not change the effect of AngII on iNOS expression;IL-6 decreased Ang II-induced iNOS protein expression(P<0.05,n=ll).Conclusions:1.Saturated fatty acid,PA,increases LV myocyte contraction in sham and hypertension Diverse responses to PA are observed in LV myocytes in hypertension;ISO+PAsignificantly enhance myocyte contraction in both groups andnormalize the contraction in two groups.2.In the presence of palmitic acid,irregular contraction of myocardial cells induced by isoproterenol-induced hypertension may be the cause of arrhythmias in hypertensive patients;3.IL-6 does not affect the positive inotropic effect of PA and PA+ISO in LV myocytes from sham and hypertensive rats.4.AngII increased the iNOS protein expression in H9C2 cells;such an effect was not affected by PA or PA+ISO.IL-6 decreased iNOS protein expression induced byAng II.