Tetrahydrobiopterin Improves Left Ventricular Diastolic Function Through PI₃K/p-Akt Signaling Pathway In Deoxycorticosterone Acetate Hypertensive Mice

Objective To elucidate whether tetrahydrobiopterin(BH4)could improves left ventricular diastolic function through phosphoinositide-3 kinase/phosphorylated protein kinase B (PI3K/p-Akt)signaling pathway in hypertensive mice.Methods Ninety male C57BL/6 mise were divided into control group(n=40) and deoxycorticosterone acetate(DOCA)-salt group(n=50). After two weeks, control group was further divided into control group(n=20) and BH4 group(n=20); DOCA-salt group was again divided into DOCA group (n=22) and DOCA+BH4 group (n=22). The blood pressures of all mice were performed three weeks later. The parameters of cardiac diastolic function were evaluated by both echocardiography and hemodynamic parameters. The myocardial cyclic guanosinc monophosphate (cGMP), malondialdehyde (MDA), superoxide dism-utase (SOD) and nitric oxide (NO) were detected by ELISA. Angiotensin Ⅱ in adtevak was tested by radioimmunoassay. The levels of BH4 and dihydrobiopterin (BH2) were mesured by high-performance liquid chromatography (HPLC). The myocardial PI3K, Akt and p-Akt expression were determined by Western blot, vascular endothelial growth factor (VEGF), Bcl-2 assaciated X protein(Bax), p-phospholamban (p-PLB), B cell lymphoma/lewkmia-2 (BCL-2), phospholamban (PLB) and sarcoplasmic or endoplasmic reticulum calcium ATPases 2 (Serca2) were experimented by immunohistochemical method. TGFβ1, α-SA and β-MHC were tested by real time -polymerase chain reaction.Results Three weeks after coarctation, comparing with the control group, systolic blood pressure (SBP) and diastolic blood pressure (DBP) were significantly increased in DOCA-salt hypertension group (P<0.01). The parameters of left ventricular diastolic function were significantly decreased (P＜0.01). The levels of BH4 and BH2 were reduced (all P<0.01). cGMP, SOD, NO and Ang Ⅱ were decreased also (P＜0.05), MDA was augmented markedly (P＜0.01). In addition, the PI3K and Akt (Ser473) protein phosphorylation in DOCA group were significantly down-regulated(P<0.01).VEGF, Bax, Phospho-PLB, PLB, and Serca2 were increased in DOCA group. TGFβ1, α-SA, β-MHC and prkce were decreased in DOCA group(P<0.05). Treatment with BH4 effectively decreased SBP, improved left ventricular diastolic function, augmented SOD, PI3K, p-Akt(Ser473), BCL-2, TGFβ1, α-SA and β-MHC in DOCA group. Treatment with BH4 reduced Ang II, VEGF, Bax, Phospho-PLB, PLB and Serca2 in DOCA group.Conclusion In early period of hypertension damages left ventricular diastolic dysfunction decreased before systolic function affected; The levels of BH4 was reduced in myocardium in hypertensive mice; Oxidative stress was involved in diastolic dysfunction in hypertensive mice, PI3K and Akt (Ser473) protein phosphorylation in hypertensive mice were decreased; That suggested that BH4 could improve left ventricular diastolic function in hypertensive mice possibly through PI3K/p-Akt signaling pathway.