Nitric Oxide Synthase Isotype Expression in Salt-Sensitive and Salt-Resistant Dahl Rats

Previous studies have suggested that salt-sensitive hypertension in humans and experimental animals may in part be due to dysregulation of the L-arginine/nitric oxide system. This study was conducted to determine the endothelial, inducible, and neuronal nitric oxide synthase expressions in the kidney, heart, aorta, and brain of salt-sensitive and salt-resistant Dahl rats. We studied salt-sensitive and salt-resistant Dahl rats maintained on high- (8%) and regular- (0.2%) salt diets for 3 weeks. Blood pressure was modestly elevated in both Dahl salt-sensitive and salt-resistant rats consuming regular diet and severely increased in sensitive but not resistant rats consuming the high-salt diet. The Dahl salt-sensitive animals showed a significant reduction in kidney, heart, and aorta inducible nitric oxide synthase protein abundance on the regular diet, with further reductions on the high-salt diet. In addition, the high-salt diet markedly downregulated endothelial nitric oxide synthase expression in the kidney and aorta but not in the heart of the Dahl salt-sensitive animals. The rise in blood pressure in the Dahl salt-sensitive rats on the high-salt diet was accompanied by a significant elevation of brain neuronal nitric oxide synthase protein. In contrast, salt-resistant animals showed no change in heart, kidney, and aorta endothelial or brain neuronal nitric oxide synthase and considerably less intense changes in inducible isotype than that seen in the salt-sensitive group in response to the high-salt diet. In conclusion, the study revealed a marked downregulation of inducible nitric oxide synthase in the Dahl salt-sensitive rats on the regular diet, with further reductions on the high-salt diet. Furthermore, Dahl salt-sensitive rats consuming the high-salt diet showed significant reductions of kidney and aorta endothelial nitric oxide synthase and an upregulation of brain neuronal nitric oxide synthase expression.