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CARDIOVASCULAR |
1 Department of Applied Physiology and Kinesiology and Center for Exercise Science, University of Florida, Gainesville, FL 32611, USA
2 Department of Physiology and Pharmacology, and the Center for Interdisciplinary Research in Cardiovascular Sciences, West Virginia University School of Medicine, Morgantown, WV 26506, USA
3 Department of Health and Kinesiology, University of Texas at Tyler, Tyler, TX 75799, USA
4 Departments of Animal Science and Medical Physiology, and The Cardiovascular Research Institute, Texas A&M University and Health Science Center, College Station, TX 77843, USA
Ageing reduces endothelium-dependent vasodilatation through an endothelial nitric oxide synthase (NOS) signalling pathway. The purpose of this study was to determine whether arginase activity diminishes endothelium-dependent vasodilatation in skeletal muscle arterioles from old rats, and whether NOS substrate (L-arginine) and cofactor (tetrahydrobiopterin; BH4) concentrations are reduced. First-order arterioles were isolated from the soleus muscle of young (6 months old) and old (24 months old) male Fischer 344 rats. In vitro changes in luminal diameter in response to stepwise increases in flow were determined in the presence of the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10–5 mol l–1), the arginase inhibitor N
-hydroxy-nor-L-arginine (NOHA, 5 x 10–4 mol l–1), exogenous L-arginine (3 x 10–3 mol l–1) or the precursor for BH4 synthesis sepiapterin (1 µmol l–1). Arteriolar L-arginine and BH4 content were determined via HPLC. Ageing decreased flow-mediated vasodilatation by 52%, and this difference was abolished with NOS inhibition. Neither inhibition of arginase activity nor addition of exogenous L-arginine had any effect on flow-mediated vasodilatation; arteriolar L-arginine content was also not different between age groups. BH4 content was lower in arterioles from old rats (94 ± 8 fmol (mg tissue)–1) relative to controls (234 ± 21 fmol (mg tissue)–1), and sepiapterin elevated flow-mediated vasodilatation in arterioles from old rats. These results demonstrate that the impairment of endothelium-dependent vasodilatation induced by old age is due to an altered nitric oxide signalling mechanism in skeletal muscle arterioles, but is not the result of increased arginase activity and limited L-arginine substrate. Rather, the age-related deficit in flow-mediated vasodilatation appears to be the result, in part, of limited BH4 bioavailability.
(Received 1 November 2007;
accepted after revision 4 December 2007;
first published online 6 December 2007)
Corresponding author M. D. Delp: Department of Applied Physiology & Kinesiology, University of Florida, Gainesville, FL 32611, USA. Email: mdelp{at}ufl.edu
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