EVIDENCE FOR TRYPTOPHAN-HYDROXYLASE AND HYDROXY-INDOL-O-METHYL-TRANSFERASE MESSENGER-RNAS IN HUMAN BLOOD-PLATELETS

Human blood platelets were tested for the presence of mRNAs coding for tryptophan hydroxylase (TPOH) and hydroxy-indol-o-methyl-transferase (HIOMT). Total RNA was extracted from platelets (12.9 +/- 3.3 mg RNA/1 00 mi blood, mean +/- SEM of 6 preparations) and cDNA synthesized by r everse transcription using random hexamers, oligo-dT or TPOH- or HIOMT -specific primers, designed to amplify a 254 bp fragment for TPOH and a 301 bp fragment for HIOMT. Positive controls were performed using RN A extracted from human normal or tumoral pineal glands. The PCR produc ts were analyzed by gel electrophoresis, transferred to a nylon membra ne and hybridized with a P-32-labeled internal probe. When random hexa mers, oligo-dT or specific primers were used for reverse transcription , amplification products of the predicted sizes were detectable follow ing electrophoresis in the case of pineal glands and following transfe r and hybridization in the case of platelets. These results show TPOH and HIOMT mRNAs to be present in human blood and support the hypothesi s that serotonin and melatonin may be synthesized in blood and, more p articularly, in platelets.