Characterization of binding sites of a new neurotensin receptor antagonist, [3H]SR 142948A, in the rat brain.
The present study describes the characterization of the binding properties and autoradiographic distribution of a new nonpeptide antagonist of neurotensin receptors, [3H]SR 142948A (2-[[5-(2,6-dimethoxyphenyl)-1-(4-(N-(3-dimethylaminopropyl)-N-methyl carbamoyl)-2-isopropylphenyl)-1H-pyrazole-3-carbonyl]-amino]-ad amantane-2-carboxylic acid, hydrochloride), in the rat brain. The binding of [3H]SR 142948A in brain membrane homogenates was specific, time-dependent, reversible and saturable. [3H]SR 142948A bound to an apparently homogeneous population of sites, with a Kd of 3.5 nM and a Bmax value of 508 fmol/mg of protein, which was 80% higher than that observed in saturation experiments with [3H]neurotensin. [3H]SR 142948A binding was inhibited by SR 142948A, the related nonpeptide receptor antagonist, SR 48692 (2-[[1-(7-chloroquinolin-4-yl)-5-(2,6-dimethoxyphenyl)-1H-pyrazole -3-carbonyl]amino]-adamantane-2-carboxylic acid) and neurotensin. Saturation and competition studies in the presence or absence of the histamine H1 receptor antagonist, levocabastine, revealed that [3H]SR 142948A bound with similar affinities to both the levocabastine-insensitive neurotensin NT1 receptors (20% of the total binding population) and the recently cloned levocabastine-sensitive neurotensin NT2 receptors (80% of the receptors) (Kd = 6.8 and 4.8 nM, respectively). The regional distribution of [3H]SR 142948A binding in the rat brain closely matched the distribution of [125I]neurotensin binding. In conclusion, these findings indicate that [3H]SR 142948A is a new potent antagonist radioligand which recognizes with high affinity both neurotensin NT1 and NT2 receptors and represents thus an excellent tool to study neurotensin receptors in the rat brain.
Betancur
C
C
INSERM U. 339, Hôpital Saint-Antoine, Paris, France. betancur@adr.st-antoine.inserm.fr
Canton
M
M
Burgos
A
A
Labeeuw
B
B
Gully
D
D
Rostène
W
W
Pélaprat
D
D
D000218:Adamantane / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism*; D008297:Male; D010880:Piperidines / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018028:Receptors, Neurotensin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014316:Tritium
D007093:Imidazoles; D010880:Piperidines; D018028:Receptors, Neurotensin; C104418:SR 142948A; D014316:Tritium; C047340:levocabastine; D000218:Adamantane