Yayoi Taniguchi

Influence of menstrual cycle on QT interval dynamics

Objectives: The aim of this study was to investigate the effects of the menstrual cycle on QT interval dynamics and the autonomic tone in healthy women.

Pioglitazone but Not Glibenclamide Improves Cardiac Expression of Heat Shock Protein 72 and Tolerance Against Ischemia/Reperfusion Injury in the Heredity Insulin-Resistant Rat

We tested the hypothesis that pioglitazone could restore expression of heat shock protein (HSP)72 in insulin-resistant rat heart. At 12 weeks of age, male Otsuka Long-Evans Tokushima Fatty (OLETF) rats and control (LETO) rats were treated with pioglitazone (10 mg · kg−1 · day−1) or glibenclamide (5 mg · kg−1 · day−1) for 4 weeks. Thereafter, hyperthermia (43°C for 20 min) was applied. In response to hyperthermia, the activation of serine/threonine kinase Akt depending on phosphatidylinositol 3 (PI3) kinase was necessary for cardiac expression of HSP72. Hyperthermia-induced activation of Akt and HSP72 expression were depressed in OLETF rat hearts. Pioglitazone but not glibenclamide improved insulin sensitivity in OLETF rats, which was associated with the restoration of Akt activation and HSP72 expression. In experiments with isolated perfused heart, reperfusion-induced cardiac functional recovery was suppressed in OLETF rat hearts, which was improved by pioglitazone but not glibenclamide. Our results suggest that PI3 kinase–dependent Akt activation, an essential signal for HSP72 expression, is depressed in the heart in insulin-resistant OLETF rats, and the results suggest also that the restoration of HSP72 expression and tolerance against ischemia/reperfusion injury by treatment with pioglitazone might be due to an improvement of insulin resistance, leading to restoration of impaired PI3 kinase–dependent Akt activation in response to hyperthermia.

Candesartan restored cardiac Hsp72 expression and tolerance against reperfusion injury in hereditary insulin-resistant rats

AIMS We tested the hypothesis that candesartan, an angiotensin II (AII) type 1 receptor antagonist, would restore the depressed phosphatidylinositol 3 (PI3) kinase-dependent Akt phosphorylation, an essential signal to induce heat-shock protein 72 (Hsp72) in response to hyperthermia, in Otsuka Long-Evans Tokushima fatty (OLETF) rats. METHODS AND RESULTS At 14 weeks of age, male OLETF rats and Long-Evans Tokushima Otsuka (LETO) rats were treated with candesartan (0.25 mg/kg/day) for 2 weeks. Thereafter, hyperthermia (43°C for 20 min) was applied. We observed the following: (i) Candesartan did not improve insulin sensitivity in OLETF rats. (ii) Candesartan restored depressed PI3 kinase-dependent Akt phosphorylation and Hsp72 expression in OLETF rat hearts. (iii) Cardiac ventricular tissue contents of AII were greater in OLETF rats, which were suppressed by candesartan. (iv) Cardiac levels of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) phosphorylation were greater in OLETF rats, which were suppressed by candesartan. In cultured cardiomyocytes, application of AII induced PTEN phosphorylation, which was suppressed by candesartan. (v) In high-fat diet insulin-resistant rats, similar results were observed with respect to Hsp72 expression, Akt phosphorylation and PTEN phosphorylation. (vi) In isolated, perfused heart experiments, reperfusion-induced cardiac functional recovery was suppressed in OLETF rat hearts, which was improved by candesartan. CONCLUSION Our results suggest that the depression of PI3 kinase-dependent Akt activation in response to hyperthermia in OLETF rats can be restored by candesartan. Substantial activation of the renin-angiotensin system, represented by increased myocardial AII content and subsequent PTEN phosphorylation, may underlie the pathogenesis which is ameliorated by candesartan.