Phenylethanolamine N-methyltransferase mRNA in rat spleen and thymus

Phenylethanolamine N-methyltransferase (PNMT), the final enzyme in the biosynthesis of epinephrine, has been detected in rat and human spleen with radioenzymatic assays, but the presence of PNMT has not been examined in other lymphoid tissues. Using the reverse transcription polymerase chain reaction (RT-PCR) and Southern blot analysis, we tested for PNMT mRNA in rat spleen and thymus. A single PCR fragment from spleen, thymus, adrenal and brainstem gave a strong hybridization signal with a PNMT cDNA probe, whereas a PCR fragment from liver was only faintly visible on Southern blots. These findings indicate that the PNMT gene is expressed in spleen and thymus and raise the possibility that lymphoid organs synthesize epinephrine as an intrinsic regulator.