Failure of dopaminergic blockade to affect prolactin, growth hormone, and cortisol responses to insulin-induced hypoglycemia in schizophrenics.

The PRL, GH, and cortisol responses to insulin tolerance tests (ITTs) were evaluated in 12 medically healthy schizophrenic patients during a drug-free period and after 1 and 6 weeks of treatment with penfluridol, a potent, long acting, dopamine-blocking neuroleptic. Hypoglycemic responses were the same before and during penfluridol therapy. Although resting PRL levels were evaluated during initial penfluridol therapy (week 1), hypoglycemia provoked a further substantial PRL increment, not significantly different in magnitude from that induced by hypoglycemia during the drug-free period. However, there was a 54% reduction (P less than 0.05) in the increase in the area under the PRL curve during week 6 compared to the drug-free period. Regarding GH and cortisol, resting levels, areas under the curve, and maximal increments after ITT were essentially the same during weeks 1 and 6 of penfluridol treatment as in the drug-free period. The failure of 1 week of dopaminergic blockade to significantly alter the hormonal (PRL, GH, and cortisol) responses to ITT in the group as a whole suggests that dopamine-blocking mechanisms play little role in mediating these responses, at least in schizophrenic patients.