Neuroendocrine aspects in monitoring of dopaminergic drugs in man.

The role of plasma homovanillic acid together with serum growth hormone and prolactin in monitoring of central dopaminergic activity was studied in healthy volunteers and psychiatric patients. Both dopaminergic agonists (apomorphine, bromocriptine and L-dopa) and antagonists (metoclopramide) were used. Apomorphine, bromocriptine and metoclopramide, which exerted the expected neuroendocrine effects caused no significant changes in plasma homovanillic acid. L-dopa increased the concentration of homovanillic acid in plasma. This effect was not potentiated by L-deprenyl, although L-dopa-induced growth hormone secretion was increased after L-deprenyl premedication. There was negative correlation between growth hormone secretion and the increase of plasma homovanillic acid after L-dopa. This indicates that the L-dopa-induced rise in plasma homovanillic acid probably reflects more peripheral L-dopa metabolism than central dopaminergic activity. Thus, it seems that plasma homovanillic acid cannot be regarded as a sensitive indicator of drug-induced changes in central dopaminergic activity in man, which is in contrast with some earlier findings in animals.