Summary
Levocabastine is a potent antihistamine drug, structurally unrelated to neurotensin. In rat and mouse brain but not in other animal species, it inhibited 60% of the [3H]neurotensin binding displaced by unlabelled neurotensin or neurotensin (8–13).
The levocabastine-sensitive site or “site 1” displayed high affinity properties for levocabastine (IC50=25 nM) and was highly stereospecific (IC50-value higher than 10 μM for one of the isomers). Binding to the “site 1” in rat brain corresponded to the [3H]neurotensin binding displaceable by 1 μM levocabastine, whereas binding to the “site 2” corresponded to the binding displaced by 1 μM neurotensin when the “site 1” was occluded by 1 μM levocabastine.
Both “site 1” and “site 2” appeared to be saturable. Scatchard plots obtained in rat bulbus olfactorius allowed to calculate a K D-values of 7.1 nM and a B max-values of 37.2 fmol/mg original tissue for “site 1”, while “site 2” displayed a K D-value of 0.7 nM and a B max-value of 16.3 fmol/mg original tissue. The regional distributions of both sites showed marked differences. The “site 1” was homogeneously distributed throughout all rat brain areas, whereas the amount of “site 2” binding was markedly different in separate brain areas: bulbus olfactorius and substantia nigra had the highest amounts (8.9 and 7.8 fmol/mg tissue) while cerebellum had the lowest (0.4 fmol/mg tissue).
In spite of its high affinity and stereospecificity, “site 1” has to be considered as an acceptor or recognition site for [3H]neurotensin because of its species-link, low saturability and homogeneous distribution in all rat brain areas.
On the other hand, “site 2” had the characteristics of a physiological receptor: high affinity, saturability in the low nanomolar range and marked regional distribution in rat brain. “Site 2” corresponds therefore most probably to the physiological neurotensin receptor. The foregoing experiments provide evidence for the presence of a drug displaceable, non-specific (=unrelated to a physiological receptor) neurotensin binding site in rat brain; levocabastine should be an important tool to occlude this site in order to reveal, by means of in vitro binding assays, the specific neurotensin binding site in rat brain.
Similar content being viewed by others
References
Bristow DR, Hare JR, Hearn JR, Martin LE (1981) Radioligand binding studies using [3H]cimetidine and [3H]ranitidine. Br J Pharmacol 72:547
Carraway R, Leeman SE (1973) The isolation of new hypotensive peptide, neurotensin, from bovine hypothalami. J Biol Chem 248:6854–6861
Carraway R, Leeman SE (1976) Characterization of radioimmunoassayable neurotensin in the rat; its differential distribution in the central nervous system, small intestine and stomach. J Biol Chem 251:7045–7052
Cooper PE, Fernstrom MH, Rorstad OP, Leeman SE, Martin JB (1981) The regional distribution of somatostatin, substance P and neurotensin in human brain. Brain Res 218:219–232
Emson PC, Goedert M, Horsfield P, Rioux F, St-Pierre S (1982) The regional distribution and chromatographic characterization of neurotensin-like immunoreactivity in the rat central nervous system. J Neurochem 38:992–999
Goedert M (1984) Neurotensin — a status report. TINS 7:3–5
Goedert M, Pittaway K, Williams BJ, Emson PC (1984a) Specific binding of tritiated neurotensin to rat brain membranes: characterization and regional distribution. Brain Res 304:71–81
Goedert M, Pittaway K, Emson PC (1984b) Neurotensin receptors in the rat striatum: lesion studies. Brain Res 299:164–168
Gorissen H, Ilien B, Aerts G, Laduron P (1980) Differentiation of solubilized dopamine receptors from spirodecanone binding sites in rat striatum. FEBS Letters 121:133–138
Kitabgi P, Kwan CY, Fox JA, Vincent JP (1984) Characterization of neurotensin binding to rat gastric smooth muscle receptor sites. Peptides 5:917–923
Laduron P (1984) Criteria for receptor sites in binding studies. Biochem Pharmacol 33:833–839
Lowry OH, Rozebrough NJ, Farr AL, Roudall RJ (1951) Protein measurement with the Folin phenol reagent. J Biol Chem 193:265–275
Mazella J, Poustis C, Labbé C, Chécler F, Kitabgi P, Granier C, van Rietschoten J, Vincent JP (1983) Monoiodo—[Trp11]neurotensin, a highly radioactive ligand of neurotensin receptors. J Biol Chem 258:3476–3481
McCann SM, Vijayan E, Koenig J, Krulich L (1982) The effects of neurotensin on anterior pituitary hormone secretion. In: Nemeroff ChB, Prange AJ (eds) Neurotensin, a brain and gastro-intestinal peptide. Ann NY Acad Sci 400:160–171
Nemeroff Ch, Cain ST (1985) Neurotensin-dopamine interactions in the CNS. TIPS May: 201–205
Palacios J, Kuhar M (1981) Neurotensin receptors are located on dopamine containing neurones in rat midbrain. Nature 294:587–589
Quirion R (1983) Interactions between neurotensin and dopamine in the brain: an overview. Peptides 4:609–615
Quirion R, Regoli D, Rioux F, St-Pierre S (1980) The stimulatory effects of neurotensin and related peptides in rat stomach strips and guinea-pig atria. Br J Pharmacol 68:83–91
Rising TJ, Norris DB, Warrander SE, Wood TP (1980) High affinity 3H-cimetidine binding in guinea-pig tissues. Life Sci 27:199–206
Sadoul JL, Kitabgi P, Rostène W, Javoy-Agid F, Agid Y, Vincent JP (1984a) Characterization and visualization of neurotensin binding to receptor sites in human brain. Biochem Biophys Res Comm 120:206–213
Sadoul JL, Chécler F Kitabgi P, Rostène W, Javoy-Agid F, Vincent JP (1984b) Loss of high affinity neurotensin receptors in substantia nigra from parkinsonian subjects. Biochem Biophys Res Comm 125:395–404
Smith IR, Cleverley MT, Ganellin CR, Metters KM (1980) Binding of [3H]cimetidine to rat brain tissue. Agents Actions 10:422–426
Stockbroekx RA, Luyckx MG, Willems JJM, Janssen MAC, Bracke JOMM, Joosen RLP, Van Wanne JP (1986) Devocabastine (R 50547), the prototype of a chemical series of compounds with specific H1-antihistaminic activity. Drug Dev Res (in press)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Schotte, A., Leysen, J.E. & Laduron, P.M. Evidence for a displaceable non-specific [3H]neurotensin binding site in rat brain. Naunyn-Schmiedeberg's Arch. Pharmacol. 333, 400–405 (1986). https://doi.org/10.1007/BF00500016
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00500016