[Downregulated PI3K-Akt-eNOS expression is related to increased atrial fibrillation inducibility in diabetic rats]

Objective: To explore the impact of PI3K-Akt-eNOS signaling on atrial fibrillation inducibility in diabetic rats. Method: Eight-week-old male diabetic rats were randomized assigned into GK group, IGF group and L-NAME group (n=8 each) which respectively received normal saline (NS), insulin like growth factor (IGF-1) or L-NAME+IGF-1 through tail vein daily for 4 weeks. Eight 8-week-old male homologous Wister-Kyoto(WKY) rats treated with intravenous NS served as control group (WKY group). Blood glucose was measured once per week. The left atrial diameter (LAD) was measured by echocardiography, the atrial electrical parameters, including the P-wave duration, the atrial effective refractory period (AERP) and its dispersion (AERP-d), the incidence and the duration of atrial fibrillation induced by atrial burst pacing, were evaluated by electro-physiological instrument at 4 weeks post various treatments. Rats were then sacrificed, left atrial (LA) cell morphology was determined on HE stained sections, LA interstitial collagen was determined on Masson stained sections. The protein expression of phosphatidylinositol 3-kinase (PI3K) and phosphate endothelial nitric oxide synthase (p-eNOS) were detected by Western blot. Results: (1) At the beginning of the study, the random blood glucose (GLU) level was significantly higher and LAD was large in GK, IGF and L-NAME groups than in WKY group;after 4 weeks, GLU level and LAD dimension of IGF group were lower than GK and L-NAME groups (P<0.01 or 0.05). (2) One rat in L-NAME group died during operation. Four weeks later, the incidence of atrial fibrillation in GK group, IGF group, L-NAME group and WKY group was 7/8, 2/8, 6/7 and 3/8. The median duration of atrial fibrillation in GK group, IGF group, L-NAME group and WKY group was 11.9(9.3, 13.1), 0(0, 1.8), 11.5(4.4, 12.0), and 0(0, 3.0) s. Compare with WKY group, the P-wave duration and PR interval were significantly longer, AERP-d, incidence, and duration of atrial fibrillation were significantly higher in GK group (P<0.01), these changed were significantly reversed in IGF group compared to GK and L-NAME groups (all P<0.01). Heart rate and AERP were similar among the 4 groups on (P>0.05). (3) Four weeks later, the CSA and CVF of LA were significantly larger in GK group than in WKY group (P<0.01), which were significantly reversed in IGF group (P<0.01 vs. GK group), and the beneficial effects of IGF disappeared by co-treatment with L-NAME (P<0.01 vs. IGF group). (4) Four weeks later, compare with WKY group, the protein expression of PI3K (P<0.01) and p-eNOS (P<0.05) of LA were significantly downregulated in GK group, which could be significantly upregulated by IGF (P<0.01 and 0.05 vs. GK group), these effects diminished by co-treatment with L-NAME (P<0.01 or 0.05 vs. IGF group). Conclusion: Increased atrial fibrillation susceptibility in diabetic rat is linked with structural and electrical remodeling in LA, possibly mediated through downregulated PI3K-Akt-eNOS signaling.