Cyclical variation of serum neutral endopeptidase lost in asthmatics: A pilot study.

Angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) are two metalloproteases, which have both been isolated from the airways. With the knowledge that young girls experience a worsening of asthma with fluctuations in oestrogen levels, we attempted to establish whether there is a change in ACE or NEP levels throughout the menstrual cycle, accounting for unhydrolysed inflammatory mediators in the airways. Asthmatics and normal controls (n=7) were studied through the follicular and luteal phases of the menstrual cycle. Peak flow rates and serum ACE levels showed no significant difference in either group. There was a four-fold increase in NEP levels in the follicular phase of normal women. Asthmatics had high levels of NEP throughout the cycle, in both the follicular and luteal phases. These results demonstrate an alteration of normal physiology in asthmatics, which might be a natural response to background inflammation.