ASSESSMENT OF THE CENTRAL DOPAMINERGIC INDEX OF PLASMA HVA IN SCHIZOPHRENIA

Under fasting conditions, the dopamine (DA) metabolite homovanillic ac id (HVA) in plasma originates mainly from central DA neurons or from c entral and peripheral noradrenergic (NA) neurons. The latter source co ntributes, in addition to HVA, the norepinephrine metabolites, for exa mple, 3-methoxy-4-hydroxyphenylglycol (MHPG). It has been shown in pri mates that the association between HVA and MHPG in plasma or urine und er varying rates elf NA metabolism can be used to obtain an estimate o f the central DA neuronal contribution of HVA to plasma or urine. This estimate is called the central dopaminergic index (CDI). Two studies presented here examine the applicability of this model in schizophreni a patients. The results were consistent with the proposed model and su ggested that only about 30 percent of the total plasma HVA concentrati ons in our patients were derived from central DA neurons. A convenient modification of this model is proposed for future studies. Since the CDI of plasma HVA is not likely to be confounded by NA activity, this tool may prove useful in disentangling the roles played by the DA and NA systems in schizophrenia.