Comparative study of nitric oxide production induced by selective estrogen receptors alpha and beta agonists in rats / Comparação da produção de óxido nítrico mediada por agonistas seletivos de receptores estrogênicos alfa e beta em ratos

BACKGROUND AND OBJECTIVES: Nitric oxide (NO) is a potent vasodilator and estrogen-mediated vasodilation that increases NO production. The association of the vascular endothelium, gender and vasodilation induced by estrogen is due to the activation of two estrogen receptors, alpha (ERa) and beta (ERb). The aim of this study was to compare NO production stimulating receptors ERa and ERb with the use of selective agonists in thoracic aortas of rats. METHODS: Aortic rings were either treated with 17 ?-estradiol (17-BE2); acetylcholine (Ach); 4,4',4-[4-propil-(1H)-pirazol-1,3,5-triyl]tris-phenol (PPT), and 2,3-Bis(4-hydroxyphenyl)-propionitrile (DPN), or left untreated, and the concentration of NO was determined by spectrophotometry method. RESULTS: The females presented a higher basal concentration of nitrite than males. PPT determined increased production of nitrite in both females and males, compared to17-beta-estradiol (17-BE2). In males, the production of nitrite induced by DPN and PPT was higher than that induced by 17-BE2. The stimulation with 17-BE2 increased the production of nitrite in females compared to males. Regardless the gender, the stimulation of aortic rings by PPT caused a greater production of nitrite compared to that induced by 17-BE2. Interestingly, the stimulation of aortic rings from males with DPN provided an increase in the nitrite production compared to the levels induced by 17-BE2 incubation. CONCLUSION: The stimulation of estrogen receptor (ER) by PPT provides greater production of nitrite than 17-BE2 regardless of gender; in males, the stimulation of ER by DPN provides bigger production of nitrite than 17-BE2; the basal production of nitrite is higher in females compared to males.

JUSTIFICATIVA E OBJETIVOS: O óxido nítrico (NO) é um potente vasodilatador e o estrógeno promove vasodilatação aumentando a produção de NO. A associação entre endotélio vascular, gênero e vasodilatação induzida pelo estrógeno, é pela ativação de receptores estrogênicos, alfa (ERa) e (beta) ERb.O objetivo deste estudo foi comparar a produção de NO estimulando receptores estrogênicos, ERa e ERb, por agonistas seletivos em aorta torácica de ratos. MÉTODOS: Anéis aórticos foram tratados com 17 ?-estradiol (17-BE2), acetilcolina (Ach), 4,4',4-[4-propil-(1H)-pirazol-1,3,5-triyl]tris-fenol (PPT) e 2,3-Bis(4-hidroxifenil)-propionitrila (DPN) ou não tratados e a determinação de NO foi feita por método espectrofotométrico. RESULTADOS: As fêmeas apresentaram produção constitutiva basal de nitrito mais elevada do que os machos. O PPT causou elevação na produção de nitrito em ambos os sexos, em relação ao observado com 17-beta estradiol (17-BE2). Nos machos, PPT e DPN, aumentaram a produção de nitrito comparada àquela induzida por 17-BE2.A estimulação com 17-BE2 causou maior produção de nitrito em fêmeas que em machos. A incubação com PPT determinou maior produção de nitrito comparada àquela induzida por 17-BE2, independente do gênero. Interessantemente, em machos,a estimulação das artérias com DPN acarretou em elevação na produção de nitrito comparada ao efeito causado por 17-BE2.CONCLUSÃO: A estimulação de receptor estrogênico (ER) pelo PPT determina maior produção de nitrito do que 17-BE2 independente do gênero; a estimulação de ER pelo DPN determina maior produção de nitrito do que 17-BE2 em machos; a produção basal de nitrito é mais elevada em fêmeas comparada aos machos.

Modulators of vascular sex hormone receptors and their effects in estrogen-deficiency states associated with menopause.

Cardiovascular disease (CVD) is more prevalent in postmenopausal than premenopausal women, suggesting vascular protective effects of estrogen. Also, experimental studies have demonstrated beneficial effects of estrogen in improving vascular function and reducing vascular injury. However, clinical trials including HERS I, HERS II, WHI and WISDOM have demonstrated minimal beneficial vascular effects of menopausal hormone therapy (MHT) in postmenopausal women with CVD. The discrepancies between the experimental findings and clinical data may be related to the vascular estrogen receptors (ER), the type, route of administration, or dosage of MHT, and subject's age. Vascular ERs mediate both genomic and non-genomic effects of estrogen on the endothelium, vascular smooth muscle (VSM), and extracellular matrix (ECM). Postmenopausal changes in vascular ER structure, polymorphisms, amount, subcellular location, affinity or signaling could modify their responsiveness to estrogen and thereby the outcome of MHT. Recent investigations and patents have been centered on developing new ER modulators and alternatives for the traditional natural and synthetic forms of MHT which carry the risk of invasive breast cancer and venous thromoboembolism. Phytoestrogens may have similar effects as traditional MHT and have not demonstrated harmful side effects. Specific estrogen receptor modulators (SERMs) such as raloxifene and tamoxifen have also been tested. ER agonists that selectively target ERalpha, ERbeta and perhaps GPR30 may modify specific vascular signaling pathways. Also, the dose, route of administration, and timing of MHT are integral to optimizing the beneficial effects and minimizing the side effects of MHT. Progesterone, testosterone and modulators of their specific receptors may also affect the overall vascular effects of MHT in estrogen-deficiency states associated with menopause.

Experimental benefits of sex hormones on vascular function and the outcome of hormone therapy in cardiovascular disease.

Cardiovascular disease (CVD) is more common in men and postmenopausal women than premenopausal women, suggesting vascular benefits of female sex hormones. Experimental data have shown beneficial vascular effects of estrogen including stimulation of endothelium-dependent nitric oxide, prostacyclin and hyperpolarizing factor-mediated vascular relaxation. However, the experimental evidence did not translate into vascular benefits of hormone replacement therapy (HRT) in postmenopausal women, and HERS, HERS-II and WHI clinical trials demonstrated adverse cardiovascular events with HRT. The lack of vascular benefits of HRT could be related to the hormone used, the vascular estrogen receptor (ER), and the subject's age and preexisting cardiovascular condition. Natural and phytoestrogens in small doses may be more beneficial than synthetic estrogen. Specific estrogen receptor modulators (SERMs) could maximize the vascular benefits, with little side effects on breast cancer. Transdermal estrogens avoid the first-pass liver metabolism associated with the oral route. Postmenopausal decrease and genetic polymorphism in vascular ER and post-receptor signaling mechanisms could also modify the effects of HRT. Variants of cytosolic/nuclear ER mediate transcriptional genomic effects that stimulate endothelial cell growth, but inhibit vascular smooth muscle (VSM) proliferation. Also, plasma membrane ERs trigger not only non-genomic stimulation of endothelium-dependent vascular relaxation, but also inhibition of [Ca(2+)]i, protein kinase C and Rho kinase-dependent VSM contraction. HRT could also be more effective in the perimenopausal period than in older postmenopausal women, and may prevent the development, while worsening preexisting CVD. Lastly, progesterone may modify the vascular effects of estrogen, and modulators of estrogen/testosterone ratio could provide alternative HRT combinations. Thus, the type, dose, route of administration and the timing/duration of HRT should be customized depending on the subject's age and preexisting cardiovascular condition, and thereby make it possible to translate the beneficial vascular effects of sex hormones to the outcome of HRT in postmenopausal CVD.