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1 Department of Internal Medicine, State University of Campinas
2 Braz Cubas University, Mogi das Cruzes, Brazil
The exposure of homeothermic animals to a cold environment leads to a powerful activation of orexigenic signalling which is accompanied by molecular and functional resistance to insulin-induced inhibition of feeding. Recent evidence suggests that AMPK participates in nutrient-dependent control of satiety and adiposity. The objective of the present study was to evaluate the effect of cold exposure upon the molecular activation of AMPK signalling in the hypothalamus of rats. Immunoblotting demonstrated that cold exposure per se is sufficient for inducing, on a time-dependent basis, the molecular activation of the serine/threonine kinase AMP-activated protein kinase (AMPK) and inactivation of the acetyl-CoA carboxylase (ACC). These molecular phenomena were accompanied by resistance to nutrient-induced inactivation of AMPK and activation of ACC. Moreover, cold-exposure led to a partial inhibition of a feeding-induced anorexigenic response, which was paralleled by resistance to insulin-induced suppression of feeding. Finally, cold exposure significantly impaired insulin-induced inhibition of AMPK through a mechanism dependent on the molecular cross-talk between phosphatidylinositol-3(PI3)-kinase/Akt and AMPK. In conclusion, increased feeding during cold exposure results, at least in part, from resistance to insulin- and nutrient-dependent anorexigenic signalling in the hypothalamus.
(Received 1 August 2005;
accepted after revision 30 August 2005;
first published online 1 September 2005)
Corresponding author L. A. Velloso: Department of Internal Medicine, Faculty of Medical Sciences (FCM), State University of Campinas (UNICAMP), Campinas-SP, 13083-970, Brazil. Email: lavelloso{at}fcm.unicamp.br
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