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Hepatic parasympathetic role in insulin resistance on an animal model of hypertension.

Ribeiro RT, Afonso RA, Macedo MP

Department of Physiology, Faculty of Medical Sciences, New University of Lisbon, Campo Mártires da Pátria, 130, 1169-056 Lisbon, Portugal.

The hepatic insulin sensitizing substance (HISS) pathway, which includes the hepatic parasympathetic nerves and hepatic nitric oxide (HNO), has been shown to be crucial to the action of insulin on glucose metabolism. Insulin resistance in essential hypertension has been related to parasympathetic dysfunction; thus, we tested the hypothesis that the HISS pathway is impaired in spontaneously hypertensive rats (SHR) when compared with their normotensive controls, Wistar (WIS) and Wistar Kyoto (WKY) rats. A modified euglycemic clamp quantified insulin sensitivity. Differentiation of the HISS-dependent and HISS-independent components of insulin action was achieved by administration of a muscarinic receptor antagonist (atropine, 3 mg/kg) or of a nitric oxide synthase inhibitor (N(g)-methyl-arginine, 0.73 mg/kg). Both SHR and WKY had lower postprandial total insulin action when compared with WIS (209.1 +/- 13.6 for WKY and 217.8 +/- 19.8 for SHR vs 296.1 +/- 16.9 mg glucose/kg body weight for WIS, P < .05). Furthermore, we observed that this is due to a decrease of the HISS-dependent component of insulin action (154.8 +/- 16.4 for WIS vs 87.1 +/- 14.5 for WKY and 55.9 +/- 15.6 mg glucose/kg body weight for SHR; P < .05 and P < .001, respectively; data concerning the atropine protocol). Blockade of HISS action by inhibition of hepatic nitric oxide synthase with N(g)-methyl-arginine showed similar results to those obtained with atropine, suggesting that they indeed act through the same pathway. In conclusion, our results support our hypothesis that impairment of the HISS pathway is responsible for the development of insulin resistance between WIS and SHR.

Published 16 January 2007 in Metabolism, 56(2): 227-33.
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