[Tetrahydrobiopterin improves left ventricular diastolic function possibly through upregulating phosphorylated protein kinase B expression in hypertensive mice induced by deoxycorticosterone acetate].

Objective: To investigate whether tetrahydrobiopterin (BH4) could improve left ventricular diastolic function through phosphoinositide-3 kinase/protein kinase B (PI3K/Akt) signaling pathway in hypertensive mice. Methods: Ten-week-old male C57BL/6 mice were used to establish the deoxycorticosterone acetate (DOCA)-salt hypertensive model, age matched Sham mice serve as the controls. Mice were divided into four groups: Sham(n=20), Sham+ BH4 (n=20), DOCA (n=22), and DOCA+ BH4 (n=22). On the 14 days after surgery, mice in Sham+ BH4 and DOCA+ BH4 groups received BH4 (0.1 ml/10 g) supplement for 7 days, while mice in Sham and DOCA groups were given equal volume of normal saline.The blood pressure measurements were performed 7 days later.Hemodynamic and echocardiographic parameters were used to assess left ventricular functions.High performance liquid chromatography (HPLC) analysis was used to measure cardiac biopterins BH4 and BH2.The phosphorylated phospholamban (p-PLB) was detected by immunohistochemical staining. PI3K, Akt and phosphorylated Akt were assayed with Western blot analysis. Results: (1) The systolic and diastolic blood pressure of DOCA group were significantly higher than control group (P<0.05). Compared with DOCA group, the systolic blood pressure was lower in DOCA+ BH4 mice (P=0.027). Diastolic blood pressure was similar between the groups. (2) Compared with Sham group, the left ventricular diastolic function indexes such as mitral annulus velocity (E') and E'/A'ratio were significantly lower, while the E/ E'ratio was significantly higher(P<0.05)in DOCA mice. The E/ E'ratio of DOCA+ BH4 group was significantly lower than that of DOCA group (P<0.05). Compared with Sham group, the left ventricular end-diastolic pressure (LVEDP), left ventricular end-diastolic pressure volumetric coefficient (EDPVR) and left ventricular relaxation time constant Tau index were significantly higher in DOCA mice (P=0.002, 0.011 and 0.016, respectively). The EDPVR and Tau index were significantly lower in DOCA+ BH4 group than in DOCA group (P<0.05). (3) Compared with Sham group, the myocardial contents of BH4 and BH2 were significantly lower in DOCA mice (P<0.05). The BH4 levels and BH4/BH2 ratio were significantly higher in Sham+ BH4 and DOCA+ BH4 groups than in the DOCA group (P<0.05), but the BH2 levels were similar between groups. (4) The cGMP content, SOD activity and NO content in the left ventricular myocardial tissue were significantly lower (P<0.05), while the MDA content was significantly higher in DOCA mice than in Sham mice.The NO content and SOD activity in DOCA+ BH4 groups were significantly higher than in the DOCA group (P<0.05). (5) Compared with DOCA group, the expression of p-PLB was significantly higher in Sham mice and lower in DOCA+ BH4 mice (P<0.05). (6) The expression of PI3K, Akt and p-Akt (Ser473 and Thr308) in DOCA mice were significantly lower than in Sham group (P<0.05). The expression of PI3K, Akt and p-Akt (Ser473) was significantly higher in DOCA+ BH4 group than in DOCA group (P<0.05). p-Akt (Thr308) expression was similar between DOCA + BH4 group and DOCA group (all P>0.05). Conclusion: Our results suggest that BH4 could improve left ventricular diastolic function in hypertensive mice, this effect might be mediated by reducing the oxidative stress in ventricular myocardium through modlating the expression of Akt and PLB phosphorylation.