EFFECTS OF ADENOSINE-ANALOGS ON APOMORPHINE-INDUCED PENILE ERECTION IN RATS

1. In the present work, the effect of adenosine agonists and antagonis ts on apomorhpine-induced penile erection (PE) has been studied. 2. Su bcutaneous (s.c.) injection of the nonselective D1/D2 dopamine recepto r agonist apomorphine (0.05-0.5 mg/kg) induced PE in a biphasic manner . The maximum effect was obtained with 0.1 mg/kg of the drug. The resp onse decreased with increasing doses of apomorphine, from 0.1 to 0.5 m g/kg. 3. Intraperitoneal (i.p.) injections of adenosine agonists 5'-N- ethylcarboxamidoadenosine (NECA) and N-6-cyclohexyladenosine (CHA) dec reased the response of apomorphine. Apomorphine-induced PE was increas ed by low doses (25, 50 mg/kg, i.p.) and decreased by high doses (75, 100 mg/kg, i.p.) of the adenosine antagonist theophylline, respectivel y. Inhibition of PE induced by NECA and CHA was antagonized by 8-PT pr etreatment. 4. Intracerebroventricular (i.c.v.) administration of CHA, NECA, and theophylline produced the same effects as i.p. injections o f these agents on PE responses. It is concluded that A-1 and A-2 adeno sine receptor activation may inhibit PE induced by dopaminergic mechan ism(s), which can be prevented by 8-PT pretreatment.