Normal prolactin responses in tardive dyskinesia.
Tardive dyskinesia has been hypothesized to be caused by a neuroleptic-induced dopamine hypersensitivity in the nigrostriatal system. This study evaluated with dopamine antagonists the possibility that such dopamine hypersensitivity extends to the tuberoinfundibular dopamine (TIDA) system, which regulates, by inhibition, pituitary prolactin secretion. Plasma prolactin concentrations in six patients with tardive dyskinesia were assessed in four conditions: During chronic haloperidol therapy; serially after abrupt haloperidol withdrawal; while unmediated; and in response to an acute dose of 0.5 mg IM haloperidol. In all four conditions, prolactin responses did not differ from those observed in normal subjects and schizophrenic patients without tardive dyskinesia. It is concluded that there is no evidence for post-synaptic dopamine hypersensitivity in the TIDA-pituitary pathway in patients with tardive dyskinesia, consistent with other reports assessing hormonal responses to dopamine agonists in such cases. It is further suggested that neuroleptic-induced dopamine hypersensitivity does not occur in the TIDA-pituitary system in humans, since it was not manifest in these tardive dyskinesia patients who would be thought particularly prone to develop it.