Cyclooxygenase-1-sensitive oxidative responses to thromboxane-prostanoid receptor activation during vascular aging and experimental menopause

Vascular aging and menopause increase cardiovascular risk in females, but the interplay among cyclooxygenase-1 (COX-1), thromboxane-prostanoid (TP) receptor signaling, nitric oxide (NO), and oxidative stress in the aging female vasculature remains unclear. We examined TP receptor-mediated responses in thoracic aortas from senescence-accelerated mouse-resistant 1 (SAMR1) and senescence-accelerated mouse-prone 8 (SAMP8) mice subjected to sham surgery (Sham), ovariectomy (Ovx), or ovariectomy followed by estradiol replacement (OvE). Aortic rings were exposed to U46619 (10-9-3x10-7 M) before and after incubation with the COX-1 inhibitor SC-560 (10-7 M), the nitric oxide synthase (NOS) inhibitor NG-nitro-L‑arginine methyl ester (L-NAME, 10-4 M), or both. Superoxide production was assessed by dihydroethidium (DHE) fluorescence after exposure to U46619 (10-8 M), with or without SC-560, and COX-1 expression was evaluated. U46619 induced concentration-dependent contractions in both strains. In Sham and OvE mice, L-NAME enhanced TP receptor-mediated contraction, whereas SC-560 exerted little effect. This L-NAME effect was blunted after ovariectomy; however, combined NOS and COX-1 inhibition significantly increased contractile responses. Ovariectomized SAMP8 mice showed the greatest TP receptor-mediated contractions, whereas estradiol replacement reduced contractile responses and restored NO-dependent modulation. U46619 increased vascular DHE fluorescence in all groups, and SC-560 attenuated this response. However, after ovariectomy, fluorescence remained significantly above basal levels despite COX-1 inhibition. COX-1 gene expression showed no major strain- or hormone-dependent differences. These findings indicate that estrogen status shapes TP receptor-mediated vascular responses by modulating NO-dependent restraint and reveal a COX-1-sensitive component of TP receptor-associated oxidative signaling in the absence of major changes in vascular COX-1 expression.