title: Endogenous modulator of dopamine receptor(s).
abstract: An endogenous modulator(s) of the dopamine receptor(s) in bovine and rat brain striatum was detected by demonstrating that water extracts of the striatum inhibited [(3)H]apomorphine binding. This modulator(s) was partially purified by methanol extraction and then successive ion exchange chromatographies on SP-Sephadex C-25 and QAE-Sephadex A-25, and gel chromatography on Sephadex G-25. The partially purified (about 1,500-fold) modulator was a fluorescamine-positive substance, Mr = 500 1000, which was heat-stable (95 degrees C, 10 min), and was destroyed by acid- and alkali-treatment, but not by treatments with various peptidases. The modulator inhibited binding of the dopamine agonist, [(3)H]apomorphine non-competitively, but did not inhibit binding of the dopamine antagonist, [(3)H]spiroperidol. Direct injection of the modulator into rat brain striatum depressed apomorphine-induced locomotor activity. Moreover the modulator inhibited dopamine-sensitive adenylate cyclase activity. These findings indicate that the modulator acts at a site(s) other than the ligand binding site of the dopamine receptor(s) and modulates the activities of dopamine agonists.
authors.affiliation: Department of Pharmacology I, Osaka University School of Medicine, Osaka 530, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Hirata
authors.forename: I
authors.initials: I
authors.lastname: Yamada
authors.forename: N
authors.initials: N
authors.lastname: Fujita
authors.forename: K
authors.initials: K
authors.lastname: Saito
authors.forename: M
authors.initials: M
authors.lastname: Nakahiro
authors.forename: H
authors.initials: H
authors.lastname: Yoshida