The effect of benztropine mesylate on the prolactin response to haloperidol.

The interaction between cholinergic and dopaminergic systems in regulating prolactin responses was investigated in normal men by administration of haloperidol (0.5 mg IM), with and without benztropine (1.0 and 2.0 mg IM). The acute prolactin response (at 30, 45, and 60 min) to haloperidol plus benztropine was significantly delayed compared to the response to haloperidol alone, in the same subjects. However, between 90 and 120 min after drug administration, prolactin responses achieved were similar in the three drug conditions. The results suggest a modest cholinergic-dopaminergic antagonism in the tuberoinfundibular system, apparent at low doses of neuroleptic and high doses of anticholinergic drugs.