Later published in Am J Physiol Heart Circ Physiol 301: H617–H624, 2011.

doi: 10.1152/ajpheart.00667.2010

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Nitric oxide (NO) is an important vasoactive molecule produced by three NO synthase (NOS) enzymes: neuronal (nNOS), inducible (iNOS) and endothelial NOS (eNOS). While eNOS contributes to blood vessel dilation that is generally thought to protect against the development of hypertension, iNOS has been primarily implicated as a disease-promoting isoform leading to protein-bound 3-nitrotyrosine formation in aortic lesions and select organs during atherogenesis. Despite this, iNOS may also play a physiological role, via the modulation of cyclooxygenase and thromboregulatory eicosanoid production. Herein, we examined the role of iNOS in a murine model of thrombosis. Blood flow was measured in carotid arteries of male and female wild-type (WT) and iNOS-deficient mice following ferric chloride-induced thrombosis. Female WT mice were less susceptible to thrombotic occlusion than male counterparts, but this protection was lost upon iNOS deletion. In contrast, male mice (with and without iNOS deletion) were equally susceptible to thrombosis. The protective effect that iNOS affords female WT mice was not associated with a change in the balance of thromboxane A2 (TxA2) and antithrombotic prostacyclin (PGI2). Our findings, however, suggest that iNOS generates a protective source of NO in female WT mice that attenuates the effects of vascular injury. Thus, although iNOS is likely detrimental during atherogenesis, physiological iNOS levels may play a protective role in preventing thrombotic occlusion, a phenomenon that may be enhanced in female mice.

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