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

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, NG-nitro-L-arginine methyl ester (L-NAME, 100 microM). 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.