sigma receptors in rat brain and testes show similar reductions in response to chronic haloperidol

The effect of haloperidol upon [3H]1,3-di-o-tolylguanidine ([3H]DTG) binding sites was assessed in rat brain and testes. An acute injection (10 mg/kg), in rats culled 2 h later, changed Kd values from 18 +/- 2 to 108 +/- 26 nM (brain) and 14 +/- 1 to 116 +/- 35 nM (testes), with unchanged Bmax values. Rats were injected with 4 mg/kg per day for 7, 14 and 21 days and culled 4 days after the last injection. By day 21, there was an average fall in Bmax for brain of 30% and for testes of 38%. Kd values remained unchanged. Thus peripheral and central [3H]DTG binding sites were reduced by chronic haloperidol in a similar way.