Effect of dopamine infusion on serum prolactin concentration in normal and hyperprolactinaemic subjects

The serum prolactin response to intravenous dopamine infusion (5 micrograms . kg-1 . min-1) was measured in twenty-one healthy subjects, in seven hyperprolactinaemic patients without evidence of a pituitary tumour, and in twenty-one patients with prolactinomas. Mean serum prolactin values were significantly suppressed in all three groups, without any significant difference between the degree of suppression. A decrease of serum prolactin to below 50% of basal values occurred in fifteen healthy subjects, in four patients without evidence of pituitary tumour, and in fourteen patients with prolactinomas. These findings demonstrate that most human prolactin-secreting pituitary adenomas are normally suppressible by exogenously administered dopamine and that dopamine infusion is not able to distinguish between tumorous and non-tumorous hyperprolactinaemia. Since intravenously infused dopamine is believed to inhibit prolactin secretion by acting at pituitary level, it is suggested that a normal functioning of pituitary dopamine receptors is maintained in most human prolactinomas.