TISSUE SOURCES OF CYTOCHROME-P450 4A AND 20-HETE SYNTHESIS IN RABBIT LUNGS

We previously reported that 20-hydroxyeicosatetraenoic acid (20-HETE) is an endogenous cytochrome P450 (cP450) 4A metabolite of arachidonic acid (AA) in human lung tissue, and is a potent cyclooxygenase-depende nt vasodilator of isolated pulmonary arteries. In the present investig ations, we identified sources of cP450 4A immunospecific protein, mess enger RNA (mRNA), and 20-HETE synthesis in rabbit lungs. Microsomes of peripheral lung tissue, airways, small and large vessels, and lysates of alveolar macrophages all express proteins of similar to 50 kD whic h cross-reacted with a primary antibody raised against rat liver cP450 4A1. Peripheral lung tissue, small and large pulmonary arteries, airw ays, and isolated vascular smooth muscle cells from small pulmonary ar teries produced 20-HETE when incubated with AA. Expression of cP450 4A 6/4A7 mRNA was readily detectable by reverse transcription-polymerase chain reaction using isoform-specific probes and 5 mu g total RNA extr acted from microdissected small pulmonary arteries. These data demonst rate that small pulmonary arteries express cP450 4A proteins and vascu lar smooth muscle cells derived from these arteries synthesize 20-HETE . Furthermore, cP450 4A appears to be widely distributed in rabbit tis sue, raising the possibility that 20-HETE generated from nonvascular t issue could serve as a paracrine factor in the pulmonary circulation.