Potent dopamine D4 receptor partial agonist (EC50 = 12.4 nM; 61% efficacy vs. dopamine). Has no agonist activity at D2 receptors (EC50 > 10 μM). Selective in rats in vivo; produces penile erection following i.c.v. administration; increases intracavernosal pressure and potentiates the proerectile effects of sildenafil following s.c. administration. Displays minimal side effects.