Autoradiographic localization of tachykinin and calcitonin gene-related peptide receptors in adult urinary bladder

Purpose: In bladder, sensory afferent nerve fibers contain the "sensory neu ropeptides" substance P (SP), neurokinin A (NKA) and calcitonin gene-relate d peptide (CGRP), which interact with tachykinin NK-1 and NK-2 receptors an d CGRP receptors, respectively. The purpose of this study was to examine th e autoradiographic distribution of these three receptor types in the human bladder, to determine whether the anatomic location of the receptors was co nsistent with their known functional roles. Materials and Methods: Specimens of urinary bladder from 9 patients (58-74 years) were obtained at cystectomy. Frozen sections of dome were labeled wi th [I-125] -Bolton-Hunter [Sar(9),Met(O-2)(11)]-SP (NK-1 receptors), [I-125 ]-[Lys(5),Tyr(I-2)(7),MeLeu(9),Nle(10)]-NKA(4-10) (NK-2 receptors) and [I-1 25]-rat CGRP-I. Binding sites were visualized using emulsion autoradiograph y. Results: NK-1 receptors were found over the endothelium of arterial blood v essels within the detrusor muscle and lamina propria, and over small vessel s in the subepithelium. NK-2 receptors were seen over the detrusor muscle a nd very sparsely over blood vessels, whereas CGRP receptors were expressed densely over the smooth muscle layer of arteries and arterioles, and weakly over collecting venules. NK-1 and CGRP receptors were not observed over th e detrusor muscle. Conclusions: Although the afferent nerves contain all three peptides, not a ll cell types express receptors for each peptide. The general distribution of receptors is in good agreement with the location of nerves, and with the known actions of SP and CGRP as vasodilator agents, and of NKA (but not SP or CGRP) in contracting the detrusor muscle.