Efeito vasorrelaxante e mecanismo de ação do 4 metilbenzoato de 4-nitrooxibutila em ratos

Abstract

Organic nitrates are known to be nitric oxide donors and potent vasodilators. Therefore, the objective was to investigate the mechanism of action of a new organic nitrate, 4-nitrooxybutyl 4-methylbenzoate (NIB7) on the vascular function of the superior mesenteric artery of rats. The ex vivo approach using compact organ bath equipment was used. Mesenteric artery rings were isolated using aerated Tyrode nutrient solution with carbogenic mixture. After stabilization, the viability of the rings was checked and the endothelium test was performed. Immediately after this, contraction was performed with phenylephrine (FEN) as well as KCl 60 mM and a concentration-response curve of NIB7 was performed to evaluate the vasorelaxant effect. Concentration-response curves of the compound were obtained in the presence of L-NAME, a non-selective NOS blocker; HDX, a NO scavenger; ODQ, soluble guanylyl cyclase (GCs) inhibitor; KCl 20mM, potassium efflux modulator; TEA 3mM, nonspecific potassium channel blocker; and blockers of specific K+ channels, voltage-operated channels (4-AP 1mM), sensitive to calcium (TEA 1mM), ATP (GLIB 1μM); and input rectifiers (BaCl2). Lastly, the rings were pre-exposed to a high concentration of NIB7 (100μM) to assess the development of vascular tolerance. The curves were obtained by non-linear regression through which pD2 and Emax were obtained. The unpaired student “t” test was performed to analyze the difference in means and “two-way” ANOVA followed by the Bonferroni post-test to analyze the concentration-response curve. Differences were considered significant when p<0.05. The NIB7 showed vasorelaxant activity independent of functional endothelium (pD2= 6,32 ± 0,11). Vasorelaxation was attenuated in rings contracted with KCl 60mM (pD2 = 5,0 ± 0,09 *p<0,05). In the presence of NO scavenger, the potency of NIB7 was attenuated (pD2 = 5,11 ± 0,08 *p<0,05). By blocking GCs, vasorelaxation was also attenuated (pD2= 3,81 ± 0,10 *p< 0,05). When incubating the rings with 20 mM KCl and 3 mM TEA, the potency was attenuated (pD2 = 5,52 ± 0,05 e 5,320 ± 0,05, respectively, *p<0.05). When investigating specific potassium channels, it was seen that in the presence of specific blockers there was no attenuation of the response. In the ex vivo pharmacological tolerance test, attenuation of potency was observed (pD2= 5,09 ± 0,10 *p<0,05). With this, it was seen that NIB7 is an NO donor, whose effect is independent of the endothelium. It suggests the involvement of the NO-GCs-PKG pathway, with the participation of potassium channels. Finally, the compound induced vascular pharmacological tolerance at the concentration used.