Effect of Heat Shock on the Vascular Reactivity and Expression of Heat Shock Protein in an Animal Model of Type 2 Diabetes Mellitus (OLETF rat)

Lee, Soon Hee; Ha, Sung Woo; Kim, Bo Wan

Abstract

BACKGROUND: Heat shock proteins (HSPs) are highly expressed in cardiovascular tissues, with heat shock possibly modulating the vascular reactivity to vasoactive agents. An abnormal vascular reactivity has been shown in diabetes, and may be closely associated to diabetic vascular complications. The aim of this study was to investigate the effects of heat shock on the vascular reactivity and the expression of HSP70 in the isolated aortae of OLETF rats, a commonly used animal model for type 2 diabetes mellitus, and LETO rats, as age matched controls.
METHODS
In 4 ring segments of the thoracic aorta isolated from each rat, the endothelium was denuded in 2 (EC-) and reserved in the other 2 (EC+). To induce heat shock, the aortic rings were exposed to 42 degrees C for 45 minutes. The vascular reactivity responses to various vasoactive agents were measured by organ chamber studies, and by changes in the HSP expression, using Western blotting of the aortic rings in the OLETF rats and controls.
RESULTS
The contractile responses to KCl became apparent 4 hours after the end of the heat shock induction. After heat shock, the phenylnephrine-induced contractile responses were similarly increased in the OLETF rats and the controls, but the increase was more significant in the EC(-) than the EC(+) rings, in both the OLETF rats and the controls. The relaxative responses to either acetylcholine (ACh) in the EC(+) aortic rings, or to sodium nitroprusside in the EC(-) rings, were not significantly affected by the heat shock treatment in either the OLETF rats or the controls, although the maximal relaxative response to ACh before the induction of the heat shock was lower in the aortic rings of the OLETF rats than in the controls. The HSP70 levels before the heat shock were higher in the aortic rings of the OLETF rats than in the controls, whereas those after heat shock were higher than those before in both the OLETF rats and the controls. The increase in the expression of HSP70 following the heat shock was higher in rings of the controls than in those of the OLETF rats. The HSP70 levels following the heat shock were increased to a greater extent in the EC(+) than the EC(-) rings of both the OLETF rats and the controls.
CONCLUSION
These results suggest that the vascular reactivity to heat shock was decreased to a greater extent in the aortae of OLETF rats than in those of the controls, and that HSP70 seems to play an important role in the vascular response to heat shock through interaction of the endothelium and the smooth muscle.