Parallelism between avoidance-suppressing and prolactin-increasing effects of antipsychotic drugs in rats

Temporal changes in the avoidance responses and serum prolactin levels were investigated for a 360 min period after s.c. administration of antipsychotic drugs such as chlorpromazine (2 mg/kg), prochlorperazine (2 mg/kg), haloperidol (0.035 mg/kg), droperidol (0.03 mg/kg), YM-09151-2 (0.005 mg/kg) and sulpiride (80 mg/kg) in rats. Male adult rats of the Wistar strain were trained under a continuous lever-press avoidance schedule (Sidman type) to observe avoidance-suppressing effects of the drugs. The avoidance response was suppressed after administration of chlorpromazine, prochlorperazine, haloperidol, droperidol and YM-09151-2, showing significant decrease in response rate and significant increase in shock rate when compared with those after saline administration, while it was scarcely suppressed within 150 min after sulpiride. On the other hand, serum prolactin levels were increased after administration of all the drugs used. Furthermore, parallelism between temporal changes in the avoidance responses and those in serum prolactin levels was observed after administration of the antipsychotic drugs, except for sulpiride. These results suggest that the prolactin-increasing effects of antipsychotic drugs are applicable for predicting antipsychotic efficacies in humans, excluding sulpiride therapy.