Different role of endothelium/nitric oxide in 17beta-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, 17beta-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. 17beta-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 17beta-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 17beta-estradiol and progesterone. In summary, the present results clearly demonstrate a different role of the functional endothelium in the relaxant response to 17beta-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 17beta-estradiol in the isolated aortas or by progesterone in the mesenteric arteries.