The lung is particularly suited to function as a “chemical filter” as it receives 100% of cardiac output and has the largest capillary endothelial surface in the body. It is involved in the modification or uptake of many vasoactive substances and hormones including serotonin, prostaglandins (E1/E2/F2alpha), norepinephrine, bradykinin. It also is the site of conversion of angiotensin I to angiotensin II – angiotensin-converting enzyme (ACE) is bound to the pulmonary endothelium. Additional non-respiratory roles include the synthesis of surfactant and production of oxygen-based free radicals for the immune system. It is not involved in the metabolism of epinephrine or histamine (in fact it can be a major source of histamine release during allergic reactions). Propofol can be metabolized in the lung but this probably does not contribute significantly to total body metabolism. Other drugs that are biotransformed or metabolized include budesonide, ciclesonide, salmeterol, fluticasone, and theophylline.