IN PATIENTS RECEIVING DOPAMINE INFUSIONS FOR TREATMENT OF SHOCK DO FREE-RADICALS CONVERT DOPAMINE TO 6-HYDROXYDOPAMINE

Free hydroxyl radicals react with dopamine in vitro to produce the neu rotoxin 6-hydroxydopamine (6-OHDA). If 6-OHDA were produced in vivo it could destroy central and/or peripheral neurons. Free radicals are pr oduced in patients with cardiovascular or toxic shock. These patients are often treated with intravenous dopamine infusions. Using a newly d eveloped method for measuring 6-OHDA in biological samples, we have ex amined blood from 15 patients receiving dopamine infusions for treatme nt of shock. 6-OHDA neither binds to nor elutes from either alumina or ion-exchange resins; therefore we used ODA-silica (Sep-Pak) to prepar e samples for HPLC analysis with electrochemical detection. 6-OHDA dis appeared rapidly from whole blood or serum at room temperature but was stable at -70-degrees-C in an HClO4 extract. Recovery from Sep-Pak wa s 950/. and detection limit 10 nmol/L. We repeated the experiments tha t showed in vitro hydroxyl radical conversion of dopamine to 5- and 6- OHDA. We detected neither 5- nor 6-OHDA in plasma samples from patient s receiving dopamine infusions at 10-28 mug kg-1 min-1. Plasma dopamin e in these patients was 1-5 mumol/L. We conclude that any 6-OHDA produ ced by hydroxyl radical attack in vivo is rapidly scavenged by endogen ous substances containing sulfhydryl groups.