In contrast, the bromocriptine-induced hypotension was fully abolished by i.v. pretreatment with metoclopramide (300 micrograms/kg), a dopamine D2 receptor antagonist that crosses the blood-brain barrier, or by combined pretreatment with i.v. and i.t. domperidone.
The present study examined whether such an amplification results from an enhanced spinal dopamine D(1) and/or D(2) receptor-mediated depressor effect.Intrathecal (i.t.) pretreatment with domperidone (40 microg/rat at T9-T10), a dopamine D(2) receptor antagonist that does not cross the blood-brain barrier, blocked nearly 35 and 56% of the maximal apomorphine-induced hypotension in control and spinal rats, respectively.The remaining hypotension after i.v. domperidone (0.5 mg/kg) pretreatment (i.e. the spinal component of the response) was significantly greater in spinal rats than in controls.