Peak expiratory nitric oxide differences in men and women: relation to the menstrual cycle.

OBJECTIVE

To develop a method to measure end expiratory nitric oxide concentration and to use it to determine whether there are sex related differences between healthy men and women.

DESIGN

Modification of commercially available chemiluminescent analyser to allow endogenous nitric oxide (endothelium derived relaxing factor) to be measured in a single slow forced vital capacity manoeuvre with evaluation of between and within subject variability. Serial measurements in women throughout the menstrual cycle.

SETTING

Specialist referral hospital.

SUBJECTS

59 healthy volunteers (40 men and 19 women).

RESULTS

Mean (SD) peak expiratory concentrations of nitric oxide in men (75 (20) ppb (parts per billion)), and women (70 (37) ppb (first measurement)) were > 5 times those previously recorded. In women concentrations at midcycle (150(39) ppb) were significantly higher (mean difference 94.9(41), P < 0.001) than during menstruation (59(25) ppb).

CONCLUSION

Nitric oxide production (endothelium derived relaxing factor activity) is influenced by cyclical hormonal changes in women. There was an increase of more than 100% at mid cycle. This may be pertinent to the lower risk of cardiovascular disease in premenopausal women.