Homovanillic acid and 5-hydroxyindoleacetic acid cerebrospinal fluid levels. A study with and without probenecid administration of their relationship to the state of consciousness after head injury.

Homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were measured in the lumbar cerebrospinal fluid of 98 patients after closed head injury. The HVA levels decreased in patients, whether or not they were given the drug probenecid, which inhibits the active transport of these acids from the brain. The decline of HVA was more notable in patients with the longest duration of unconsciousness. The HVA levels showed no correlation with the state of consciousness at the moment of the lumbar puncture. The 5-HIAA levels were below normal in the conscious patients, but paradoxically, at about normal levels in unconscious patients. The overall results suggest a decreased cerebral dopamine and serotonin metabolism after head injury.