EVIDENCE FOR A PATHOLOGICAL REDUCTION IN BRAIN DOPAMINE METABOLISM IN IDIOPATHIC HYPERPROLACTINEMIA

The role of brain catecholamine activity in the neuroendocrine regulation of the dopamine-PRL system in idiopathic hyperprolactinemia was investigated by high-performance liquid chromatography with electrochemical detector. We measured urinary dopamine, norepinephrine, epinephrine, vanillylmandelic acid, homovanillic acid, 3,4-dihydroxyphenylacetic acid and total 3-methoxy-4-hydroxyphenylglycol levels in 12 women with idiopathic hyperprolactinemia before and during either peripheral dopa-decarboxylase blockade, by carbidopa, or dopamine beta-hydroxylase blockade, by disulfiram. Homovanillic acid and 3,4-dihydroxyphenylacetic acid concentrations were significantly lower (p < 0.001 and p < 0.005, respectively) in patients with idiopathic hyperprolactinemia compared with those in 12 control subjects in the early follicular phase, whereas they were similar to those in the control subjects in the pre-ovulatory phase. Dopamine, norepinephrine, epinephrine, vanillylmandelic acid and 3-methoxy-4-hydroxyphenylglycol concentrations were similar to those of the control subjects in both phases of the cycle. During carbidopa administration the levels of all urinary catecholamines and metabolites were unchanged, except that of dopamine which dropped remarkably (p < 0.001). During disulfiram administration dopamine, homovanillic acid and 3,4-dihydroxyphenylacetic acid concentrations increased (p < 0.05, p < 0.001 and p < 0.005, respectively) and those of norepinephrine, vanillylmandelic acid and 3-methoxy 4-hydroxyphenylglycol decreased (p < 0.05, p < 0.001 and p < 0.005, respectively), whereas epinephrine levels remained unaltered. These data support the existence of a quantitatively reduced brain dopamine activity in idiopathic hyperprolactinemia.