Clozapine increases rat serum prolactin levels

Clozapine differs from other anti-psychotic drugs in that is produces little or no extrapyramidal side effects. The effects of clozapine on rat brain dopamine differ markedly from those of the neuroleptic drugs. The neuroleptics increase rat serum prolactin levels which has been attributed to their dopamine receptor blocking properties. We found that clozapine markedly increased serum prolactin levels in male rats when injected intraperitoneally in doses of 5, 10, 50 and 100 mg/kg. Serum prolactin levels after 5 mg/kg clozapine were significantly less than in rats given 10, 50 and 100 mg/kg which did not significantly differ from each other. Serum prolactin after 10 mg/kg clozapine was significantly greater than after chlorpromazine, 5 mg/kg and haloperidol, 0.5 mg/kg. The increases in serum prolactin are attributed to clozapine's ability to produce dopamine blockade or to inhibit nerve impulse-dopamine release, or both. The capacity of clozapine to affect brain serotonin and norepinephrine metabolism and its strong anti-cholinergic properties are probably not involved in its ability to increase serum prolactin.