EFFECTS OF CHRONIC LITHIUM PRETREATMENT ON APOMORPHINE-INDUCED PENILEERECTION

1. The effects of chronic lithium pretreatment (600 mg/l in drinking r ats, 30 days) on penile erection (PE) induced by apomorphine were inve stigated in rats. This treatment resulted in a serum Li concentration after 30 days of 0.31 +/- 0.01 mmol/l. 2. Subcutaneous (s.c.) administ ration of mixed D1/D2 dopamine receptor agonist apomorphine (0.05-0.5 mg/kg) induced PE in a biphasic manner. The maximum effect was obtaine d with 0.1 mg/kg of the drug while the response decreased with increas ing doses of apomorphine from 0.1 to 0.5 mg/kg. 3. Pretreatment of ani mals with 0.0125-0.1 mg/kg of D1 dopamine receptor antagonist SCH 2339 0 or D2 dopamine receptor antagonist sulpiride (12.5-100 mg/kg) decrea sed apomorphine-induced PE. Combination of SCH 23390 (0.025 mg/kg) wit h sulpiride (12.5 mg/kg) caused a stronger inhibitory effect on apomor phine response. This indicates that both D1 and D2 dopamine receptors may be involved in PE induced by apomorphine. 4. The response induced by apomorphine (0.05-0.5 mg/kg) was decreased in animals pretreated wi th chronic lithium. The inhibitory effect of sulpiride on apomorphine response, increased in animals pretreated with lithium, in contrast th e inhibitory effect of SCH 23390 did not change in this condition. How ever, a combination of SCH 23390 with sulpiride increased inhibitory e ffect on apomorphine response in lithium pretreated rats. 5. It is con cluded that chronic lithium inhibits PE induced by dopaminergic mechan ism(s).