The sensitivity of the dopaminergic hypothalamic pituitary system, as indicated by growth hormone (GH) release after apomorphine (0.5 mg SC), was studied in 11 chronic schizophrenic in-patients under long-term neuroleptic (NL) therapy and after 12 and 30 days' drug withdrawal. GH peak levels after a 12-day drug-free period were significantly elevated (13.1 +/- 12 ng/ml) as compared to NL therapy (4.6 +/- 6.1 ng/ml). Controls showed a significant higher mean peak GH response (13.6 +/- 10 ng/ml) compared to chronic schizophrenic patients under long-term NL therapy. The GH response of patients with symptoms of tardive dyskinesia (TD) did not differ significantly from that of patients without signs of TD. The prolactin (PRL) serum levels under long-term NL treatment were within the normal range in male schizophrenics but decreased significantly after 12 days' drug withdrawal. The data presented indicate a reduced sensitivity of the hypothalamic-pituitary dopamine receptors under long-term NL therapy. The significant increase in GH response on day 12 probably corresponds to a readjustment from a mostly blunted GH response under NL therapy back to stimulated levels of normal controls. No supersensitivity of the pituitary dopamine receptors could be detected.
