Endocrine responses to tryptophan infusion in schizophrenic patients treated with neuroleptics

The growth hormone (GH) and prolactin (PRL) responses to intravenous L-tryptophan (LTP) were measured in 20 schizophrenics receiving long-term treatment with neuroleptics and 20 unmedicated control subjects. In the patients, the PRL response was significantly enhanced, and it correlated with PRL baseline concentration. In contrast, the patients' GH response was markedly reduced. These opposite changes in PRL and GH responses to LTP are unlikely to be accounted for by the effect of neuroleptics on serotonin receptors, but they may have been due to the blockade of DA receptors, which is known to disinhibit PRL release and to suppress that of GH.