Abnormal prolactin responsivity to dopaminergic suppression in hyperprolactinemic patients

Previous in vivo studies have shown that the constant infusion of dopamine suppresses prolactin (PRL) levels to within the normal range in a variety of hyperprolactinemic states, but there are no data on the relative suppressibility of the lactotroph in patients with hyperprolactinemia or on their metabolism of dopamine. Consequently, six patients with elevated PRL levels received a dopamine infusion of 4 μg/kg/min to study PRL clearance while another eight patients underwent a graded infusion at rates of 0, 1, 2 and 4 μg/kg/min to test PRL suppressibility. In four patients of the latter group an 8 μg/kg/min infusion rate was added. Healthy volunteer control subjects underwent comparable studies. PRL was measured by radioimmunoassay and dopamine by radioenzymatic techniques. The absolute PRL levels at each infusion rate were greater in the patients than in the control subjects. During the 4 μg/kg/min infusion rate, the respective PRL concentrations were 8.2 ± 1.8 and 2.0 ±0.1 ng/ml, (p