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

The serum prolactin response to intravenous dopamine infusion (5 μg.kg ^-1.min ^-1) was measured in 21 healthy subjects, in 7 hyperprolactinemic patients without evidence of a pituitary tumor, and in 21 patients with prolactinomas. Mean serum 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 15 healthy subjects, in 4 patients without evidence of pituitary tumor, and in 14 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 hyperprolactinemia. 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.