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This Article Full Text Full Text (PDF) All Versions of this Article: 297/5/H1767    most recent 00536.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Kobayashi, T. Articles by Kamata, K. PubMed PubMed Citation Articles by Kobayashi, T. Articles by Kamata, K.

Activation of the PDK-1/Akt/eNOS pathway involved in aortic endothelial function differs between hyperinsulinemic and insulin-deficient diabetic rats

Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Tokyo, Japan

Submitted June 12, 2009 ; accepted in final form August 27, 2009

In diabetic states, altered plasma insulin is likely to play key roles in 3-phosphoinositide-dependent protein kinase (PDK)/Akt pathway activation, in insulin resistance and in endothelial dysfunction. Since the molecular mechanism(s) remains unclear, we examined the relationship between the PDK/Akt/endothelial nitric oxide synthase (NOS) pathway and endothelial function in aortas from diabetic rats that were either insulin deficient or hyperinsulinemic. Untreated diabetic (diabetic) rats exhibited hyperglycemia and hypoinsulinemia, whereas high-insulin-treated diabetic (HI-diabetic) rats exhibited hyperinsulinemia. Aortas from the diabetic group displayed impaired endothelium-dependent relaxation in response to ACh, whereas the insulin-induced relaxation was increased. In HI-diabetic aortas, the ACh-induced relaxation was normal, but that induced by insulin was impaired. The insulin-induced relaxation was inhibited by treatment with an Akt inhibitor in control and diabetic aortas, but not in the HI-diabetic aorta. This inhibitory effect on insulin-induced relaxation was greater in diabetic aortas than in control aortas. In all groups, ACh-induced relaxation was unaffected by the above inhibitor. In the diabetic group, various insulin-stimulated levels (nitric oxide production, phosphorylation of endothelial NOS at Ser¹¹⁷⁷, of Akt at Thr³⁰⁸, and of PDK-1 at Ser²⁴¹) were significantly increased, whereas, in the HI-diabetic group, these levels were all decreased (vs. control aortas). These results suggest that the plasma insulin level has a close relation to the level of aortic PDK-1/Akt (at Thr³⁰⁸)/NOS activities, and that reduced actions of the PDK-1/Akt (at Thr³⁰⁸) signal pathway may contribute to the impairments of insulin-induced endothelial functions seen in hyperinsulinemic diabetes.

hyperinsulinemia; diabetes; nitric oxide; 3-phosphoinositide-dependent protein kinase