title: Specific substance P binding sites in rat thymus and spleen: in vitro autoradiographic study.
abstract: Substance P binding sites were localized in rat thymus and spleen by incubation of tissue sections with [125I]Bolton-Hunter substance P, [3H]Ultrofilm autoradiography with image analysis coupled to computerized microdensitometry and comparison with 125I standards. The tissue localization of the binding sites was determined with emulsion autoradiography. A single type of specific, saturable, high affinity binding sites was found associated with the vasculature in the medulla of the thymus and the marginal sinus of the spleen, with a Kd of 0.10 and 0.14 nM, respectively. Of all the unlabeled tachykinins tested (substance P, physalaemin, substance K, eledoisin, kassinin, and neuromedin K) substance P was the most potent inhibitor of [125I]Bolton-Hunter substance P binding, with an IC50 of approximately 0.5 nM, indicating the presence of substance P-P binding sites. Our results support the hypothesis of a role for substance P in the modulation of the immune system.
mesh_terms: D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013154:Spleen / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism*; D013388:Succinimides / Q000378:metabolism; D013950:Thymus Gland / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: C043194:Bolton Hunter reagent-substance P conjugate; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter; D013388:Succinimides; D013373:Substance P