Different role of endothelium/nitric oxide in 17β-estradiol- and progesterone-induced relaxation in rat arteries

The present study was aimed to examine the different role of endothelium/nitric oxide in relaxation induced by two female sex hormones, 17β-estradiol and progesterone in rat isolated aortas and mesenteric arteries. The isometric force of each ring was measured with Grass force-displacement transducers in the organ bathes. 17β-Estradiol induced both endothelium-dependent and -independent relaxation in the rat aortas but only the endothelium-independent relaxation in the rat mesenteric arteries. In contrast, progesterone induced both endothelium-dependent and -independent relaxation in the rat mesenteric arteries but only endothelium-independent relaxation in rat aortas. N^G-Nitro-L-arginine methyl ester and methylene blue attenuated the relaxant response to 17β-estradiol in the aortic rings or to progesterone in the mesenteric arteries. Pretreatment with L-arginine antagonized the effect of N^G-nitro-L-arginine methyl ester on sex hormone-induced relaxation. The endothelium contribution to relaxation seems to only relate to lower concentrations of 17β-estradiol and progesterone. In summary, the present results clearly demonstrate a different role of the functional endothelium in the relaxant response to 17β-estradiol or progesterone in the conduit vessel (aorta) and the resistance vessels (mesenteric artery). Nitric oxide contributes largely to the endothelium-dependent relaxation induced by 17β-estradiol in the isolated aortas or by progesterone in the mesenteric arteries. © 2001 Elsevier Science Inc. All rights reserved.