Dose and sex related effects of aromatic aminoacids decarboxylase inhibitors on serum prolactin in humans

Single doses of carbidopa and benserazide, two inhibitors of aromatic aminoacids decarboxylase, have been given orally to healthy women and men aged 19 to 32 years. Serum prolactin levels increased in respect to baseline levels when 80, 125 or 250 mg of carbidopa and 10, 20, 30, 50, 80 or 125 mg of benserazide were given. The carbidopa doses of 20 and 50 mg were ineffective. Carbidopa induced the enhancement of serum prolactin at a later time and over a longer time span than benserazide. The effect on serum prolactin is dose dependent for both drugs. The hyperprolactinaemia obtained with 250 mg of carbidopa and with 125 mg of benserazide is significantly larger in women than in age matched men. The observed prolactin increase fits with the hypothesis that a diminution of the inhibitory effect of dopamine at the pituitary and/or at the median eminence levels may occur in connection to the pharmacologically impaired monoamine synthesis. An effect of serotonin cannot, however, be excluded.