Comparison of neuroleptic binding characteristics in rat striatum and renal cortex.
The binding characteristics of the dopaminergic ligand, 3H-spiperone, were compared in renal cortical and striatal membrane homogenates of the rat. This ligand labelled a single class of high affinity binding sites in striatum with an apparent dissociation constant (Kd) of 0.13 nM and a maximal number of binding sites (Bmax) of 890 fmol/mg protein representing D-2 receptors. In the renal cortex, 3H-spiperone identified a population of binding sites with a Bmax and a Kd of 310 fmol/mg protein and 5.1 nM, respectively. The antagonist displacing profile suggests the dopaminergic nature of the renal binding site. The affinities of dopamine antagonists for the peripheral 3H-spiperone binding site were in general in the micromolar range while the affinities of D-2 or D-2/D-1 dopamine antagonists in striatum were in the nanomolar range. Moreover, these sites showed differential stereoselectivity for (+)- and (-)-isomers of sulpiride. In conclusion, the presence of a D-2/DA-2 dopamine receptor population in renal cortex could not be confirmed. The pharmacological properties of the peripheral 3H-spiperone binding site are also different from the DA-1 receptor but seem to resemble those previously reported for dopamine receptors in sympathetic ganglia and adrenal medulla.
Hietala
J
J
Department of Pharmacology, University of Turku, Finland.
Syvälahti
E
E
Röyttä
M
M
D000818:Animals; D003342:Corpus Striatum / Q000378:metabolism*; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000032:analysis; D013134:Spiperone / Q000378:metabolism*; D013237:Stereoisomerism; D013469:Sulpiride / Q000378:metabolism
D011954:Receptors, Dopamine; D013134:Spiperone; D013469:Sulpiride