The effect of ovariectomy on depressed contractions to phenylephrine and KC1 and increased relaxation to acetylcholine in isolated aortic rings of female compared to male rabbits

Abstract

1 Differences in vascular responses to phenylephrine, acetylcholine (ACh) and potassium chloride (KCl) were studied in rabbit aorta from female and male rabbits, in the absence and presence of an inhibitor of nitric oxide (NO) production, N0-nitro-L-arginine methyl ester (L-NAME, 100 yM).2 Phenylephrine and KCl-induced contractions, were significantly reduced in amplitude (P<0.01) in the rings from female rabbits compared to those from male rabbits. 3 ACh-induced relaxation was greater (P<0.01) in aortic rings from females than from males. 4 Incubation of the rings with L-NAME abolished the phenylephrine-induced contraction differences between rings from male and female rabbits. 5 Ovariectomy eliminated the differences in vascular responses to phenylephrine, KCl and ACh of aortic rings from the female rabbits. 6 Both basal and ACh-stimulated release of nitrites from aortic rings was greater (P<0.01) in vascular tissue from female than male rabbits. 7 These results indicate that differences in vascular reactivity in aortic rings from male and female rabbits may be associated with a higher release of NO, resulting in an increased vasodilator response in the female rabbits.

Role of gender and vascular endothelium in rat aorta response to 17 b -estradiol

“…More importantly, there is a more pronounced endotheliumdependent relaxation component of 17β-estradiol, which is particularly evident in female rats. This also has been seen in female rabbit aorta, in which it was suggested that tissues from female animals have higher capacity to release vasodilator substances compared with their male counterparts (Sanchez et al 1996). Our study actually reports that the overall magnitude in relaxation response in male endothelium-intact aorta did not significantly differ from that in the female endothelium-intact aorta.…”

“…These experiments were conducted in the absence of both β-adrenoceptor blockade and inhibition of prostanoid synthesis, therefore it is likely that higher concentrations of noradrenaline could activate vasodilatory β-adrenoceptors and vasodilatory prostaglandin release. The differences between female and male endothelium-intact aortic response to noradrenaline relates to enhanced nitric oxide production in the female endothelium (Sanchez et al 1996).…”

“…Furthermore, it has been implied that differences exist between male and female with respect to endothelial modulation, which most likely involves a differential release of nitric oxide. In support of this, nitric oxide synthase might be regulated by sex hormones (Sanchez et al 1996). This suggests that estrogen may exert its beneficial effect at the level of nitric oxide synthase.…”

Sex differences in the relative contributions of nitric oxide and EDHF to agonist‐stimulated endothelium‐dependent relaxations in the rat isolated mesenteric arterial bed

“…Hayashi et al . (1992) and Sánchez et al . (1996) both observed an enhanced basal and acetylcholine‐stimulated nitrite release from the aorta of female rabbits and rats compared to male controls, suggesting a greater release of NO.…”

“…However, it is clear from these latter studies that there exists sex differences in endothelium‐dependent regulation of vascular smooth muscle tone. Endothelium‐dependent vasorelaxation responses to acetylcholine in isolated aortae of the rat and rabbit have been demonstrated to be greater in the aortae from females compared to males (Hayashi et al ., 1992; Kauser & Rubanyi, 1993; 1994; Sánchez et al ., 1996). Hayashi et al .…”