Cigarettes are bad, and not just for your lungs

Positron emission tomography (PET) images of the concentration of the enzyme MAO-B (monoamine oxidase B) in the body of a healthy control and of a cigarette smoker (fairly heavy smokers, ~ 1 pack/day). There are significant decreases in the concentration of the enzyme throughout the body of the smoker. These subjects were scanned with L-[11C]deprenyl, and scanning was started at 25-min post-radiotracer injection. Red is the highest radiotracer concentration on the color scale, and images are scaled so that they can be compared directly.

Reduced MAO-B in peripheral organs could potentially alter sympathetic tone, and could enhance levels of MAO-B-specific substrates, including endogenous substrates and dietary amines as well as those released by nicotine in tobacco smoke.

Source, mentioned in this review.