1. Dopamine receptor occupancy in vivo: measurement using N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ)
C F Saller, L D Kreamer, L A Adamovage, A I Salama Life Sci. 1989;45(10):917-29. doi: 10.1016/0024-3205(89)90206-3.
N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) inactivates a variety of monoamine neurotransmitter receptors. In this report, protection against EEDQ-induced inactivation of D-1 and D-2 DA receptors by DA antagonists and agonists was used to obtain a measure of occupancy of these receptors in vivo by such drugs. Rats were pretreated with drugs and then given EEDQ (10 mg/kg, i.p.). Twenty-four hours after the EEDQ injections, the animals were decapitated and the number of receptors remaining was measured using conventional receptor binding assays. The D-1 antagonist SCH 23390 potently protected D-1 sites from EEDQ-induced inactivation in a dose-dependent manner. Similarly, NO-756, another D-1 antagonist, selectively protected D-1 sites from inactivation. Conversely, haloperidol, a relatively selective D-2 antagonist, protected D-2 sites from inactivation. Likewise, a number of antipsychotic DA antagonists also protected D-2 sites from inactivation. Clozapine, fluperlapine, and (+) butaclamol were effective at protecting both D-1 sites and D-2 sites. In addition, the D-1 agonist SKF 38393 protected D-1 sites from EEDQ-induced inactivation, whereas the D-2 agonist quinpirole protected D-2 sites. (-) Apomorphine, a mixed D-1/D-2 agonist, protected both sites. Thus, this type of method provides a simple means of evaluating the occupation of DA receptors by DA antagonists and agonists in vivo.
2. Inactivation of D1 and D2 dopamine receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline in vivo: selective protection by neuroleptics
E Meller, K Bohmaker, M Goldstein, A J Friedhoff J Pharmacol Exp Ther. 1985 Jun;233(3):656-62.
Treatment of rats with the peptide coupling agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (6 mg/kg i.p.) irreversibly reduced the binding of [3H]spiperone ([3H]SPIP) and cis-[3H] piflutixol to striatal D2 and D1 receptors, respectively, by 70 to 75%. In each instance only the receptor density was affected, without a change in the dissociation constant (Kd) of either radioligand. Pretreatment with sulpiride (200 mg/kg i.p.), a selective D2 antagonist, preferentially protected [3H]SPIP sites against N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline-induced inactivation, whereas pretreatment with SCH 23390 (3 mg/kg i.p.), a putative selective D1 antagonist, preferentially blocked the inactivation of cis-[3H]piflutixol binding sites. N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline markedly reduced radioligand binding to cortical alpha-1 ([3H]prazosin) and alpha-2 [( 3H]yohimbine) receptors (10-20% of control) but had a lesser effect on serotonin-2 ([3H]SPIP) and serotonin-1 ([3H]5-HT) receptors (30-40% of control). Muscarinic cholinergic ([3H] quinuclidinyl benzilate) and beta adrenergic ([3H]dihydroalprenolol) receptors were only slightly affected. None of these nondopaminergic sites were protected by sulpiride or SCH 23390, with the exception of serotonin-2 and serotonin-1 which were partially protected by the latter. SPIP (0.2 mg/kg i.p.), haloperidol (1 mg/kg i.p.) and pimozide (2 mg/kg i.p.) all selectively protected the D2 receptor, whereas cis-flupenthixol (2 mg/kg i.p.) protected both dopamine receptors; its inactive isomer trans-flupenthixol (20 mg/kg i.p.) protected neither. Bulbocapnine (25 mg/kg s.c.) selectively, but partially, protected the D1 site.(ABSTRACT TRUNCATED AT 250 WORDS)
