EFFECT OF (-)-STEPHOLIDINE ON SERUM PROLACTIN LEVEL OF FEMALE RATS

AIM: To study the effect of (-)-stepholidine (SPD) on serum prolactin (PRL) level and elucidate its pharmacological action on,dopamine D-2 r eceptors. METHOD: After ip administration of dopamine receptor agonist , antagonist, or SPD, the serum PRL levels were determined by radioimm unoassay. RESULTS: SPD (24 mg . kg(-1), ip) caused a rapid rise in ser um PRL level, lasting more than 1 h. SPD 0.2-40 mg . kg(-1) raised ser um PRL level in a dose-dependent manner with ED(50) of 3.7 mg . kg(-1) (95 % confidence limits, 2.6-4.3 mg . kg(-1)) and PRL maximal level o f 448 +/-64 mu g . L(-1). Pergolide 2 mg . kg(-1) ip caused a decrease (P < 0.01 vs saline) of PRL level, which was partially attenuated by SPD of 5 mg . kg(-1) and completely abolished by 10 mg . kg(-1). CONCL USION: SPD is a dopamine D-2 receptor antagonist.