title: (-)-Stepholidine antagonizes the inhibition by D2 receptor agonists on synaptosomal tyrosine hydroylase in rat corpus striatum.
abstract: OBJECTIVE
  To evaluate the action of (-)-stepholidine (SPD), a novel dopamine (DA) receptor antagonist, on inhibition by presynaptic D2 receptor agonists on the activity of synaptosomal tyrosine hydroxylase (TH) in the striatum.
  
  
  METHODS
  The TH activity was measured by HPLC-ECD.
  
  
  RESULTS
  The mixed DA receptor agonist apomorphine (Apo 10.4 nmol L-1) and selective D2 receptor agonists N-0437 (0.4 pmol L-1) and quinpirole (0.8 mumol L-1) inhibited the activity of TH, while selective D1 receptor agonist SKF 38393 (0.001-10 mumol L-1) and SPD (1-100 mumol L-1) failed to inhibit the TH activity. The inhibition of N-0437 and quinpirole were antagonized by D2 receptor antagonist spiperone and SPD.
  
  
  CONCLUSIONS
  The negative feedback regulation of presynaptic DA receptors is mediated via D2 receptors and SPD is an antagonist on presynaptic D2 DA receptors.
authors.affiliation: Shanghai Institute of Materia Medica, Chinese Academy of Sciences.
authors.forename: G
authors.initials: G
authors.lastname: Hu
authors.forename: G Z
authors.initials: GZ
authors.lastname: Jin
mesh_terms: D000818:Animals; D001599:Berberine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003342:Corpus Striatum / Q000201:enzymology*; D018492:Dopamine Antagonists / Q000494:pharmacology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000819:agonists*; D013574:Synaptosomes / Q000201:enzymology; D014446:Tyrosine 3-Monooxygenase / Q000187:drug effects* / Q000378:metabolism
chemical_list: D018492:Dopamine Antagonists; D017448:Receptors, Dopamine D2; D001599:Berberine; C010513:stepholidine; D014446:Tyrosine 3-Monooxygenase