Now that is a very interesting question! Unfortunately, I don't think that we have a complete answer. A couple of notes, that perhaps can provide some perspective:
1. lungs are highly vascularised areas with a large amount of vascular endothelium, making them a great location to express ACE if you want to convert as much angiotensin I as you can in the space of a heartbeat (which you'd like to do if your blood pressure dropped, for example).
2. ACE is not specific for angiotensin, it acts on a variety of peptides. Bradykinin is a good example as it can provide more perspective on why ACE is expressed mainly in lung tissue. Bradykinin acts to contract smooth muscle in your airways. Thus, degrading bradykinin via ACE is a good way to improve your breathing.
1. lungs are highly vascularised areas with a large amount of vascular endothelium, making them a great location to express ACE if you want to convert as much angiotensin I as you can in the space of a heartbeat (which you'd like to do if your blood pressure dropped, for example).
2. ACE is not specific for angiotensin, it acts on a variety of peptides. Bradykinin is a good example as it can provide more perspective on why ACE is expressed mainly in lung tissue. Bradykinin acts to contract smooth muscle in your airways. Thus, degrading bradykinin via ACE is a good way to improve your breathing.