Failure of dopaminergic blockade to affect prolactin, growth hormone, and cortisol responses to insulininduced 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 elevated during initial penfluridol therapy (week 1), hypoglycemia provoked a further substantial PRL increment, not significantly different in magnitude from that induced by hypoglycemia during thedrug-free period. However, there was a 54% reduction (P < 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.