Characterization of the radioiodinated analogue of SCH 23390: in vitro and in vivo D-1 dopamine receptor binding studies.

Published

Journal Article

A new radioiodinated molecule, 125I-SCH 38840 (previously referred to as 125I-SCH 23982), has been recently reported to be a D-1 dopamine receptor ligand. The current study confirms and expands the characterization of both the radiolabeled and unlabeled forms of this compound, as well as describing the development of an in vivo D-1 receptor binding assay utilizing the 125I-SCH 38840. The binding of 125I-SCH 38840 to rat striatal membranes, in vitro, was saturable and exhibited a KD of 1.47 nM. Competition studies using 125I-SCH 38840 exhibited a pharmacological profile consistent with the proposal that 125I-SCH 38840 was binding to the D-1 receptor. Further studies with the unlabeled SCH 38840 demonstrated that it inhibited dopamine-stimulated adenylate cyclase with a KI of 66.1 nM, indicating that SCH 38840 was acting as a D-1 antagonist. Behavioral studies demonstrated that SCH 38840 (MED = 1.0 mg/kg, s.c.) blocked conditioned avoidance responding in rats, a measurement considered predictive of anti-psychotic activity in man. In vivo binding of 125I-SCH 38840 to rat striatum following s.c. administration was specific. Peak striatal levels were observed 1 h after injection, with measurable binding observed out to 8 h post-treatment. The displacement of the in vivo binding by unlabeled standards again suggested a D-1 selective interaction. The half-life of the in vivo binding of 125I-SCH 38840 was approximately 1.25 h, and was nearly equivalent to the half-life of the anti-CAR activity of unlabeled SCH 38840. These results clearly demonstrate the D-1 nature of SCH 38840's behavioral activity and strengthen the anti-psychotic potential of a D-1 antagonist.

Full Text

Duke Authors

Cited Authors

  • McQuade, RD; Chipkin, R; Amlaiky, N; Caron, M; Iorio, L; Barnett, A

Published Date

  • January 1988

Published In

Volume / Issue

  • 43 / 14

Start / End Page

  • 1151 - 1160

PubMed ID

  • 3050344

Pubmed Central ID

  • 3050344

Electronic International Standard Serial Number (EISSN)

  • 1879-0631

International Standard Serial Number (ISSN)

  • 0024-3205

Digital Object Identifier (DOI)

  • 10.1016/0024-3205(88)90474-2

Language

  • eng