Effect of capsaicin on distribution of binding sites for tachykinins and calcitonin gene-related peptide in rat urinary bladder: a quantitative autoradiographic study.

The autoradiographic localization of binding sites for [125I]BH-[Sar9,Met(O2)11]SP, [125I]NKA, and [125I]CGRP was investigated in adjacent sections of urinary bladder body, from adult rats pretreated 14 days before with capsaicin or vehicle. Location of silver grains was assessed both qualitatively and quantitatively using computerized densitometry. Dense labeling of smooth muscle was seen with both [125I]BH-[Sar9,Met(O2)11]SP ([125I]BHSar-SP) and [125I]NKA; in addition, [125I]BHSar-SP labeled submucosal blood vessels. For these radioligands, no differences were apparent between sections from capsaicin- and vehicle-pretreated rats. Specific binding of [125I]CGRP was observed over the epithelium and weakly over submucosal arterioles, but not over smooth muscle. The density of [125I]CGRP binding sites on the epithelium, but not blood vessels, was increased (p < 0.05) by 22% after chronic capsaicin pretreatment, suggesting receptor upregulation. This study demonstrates that although all three peptides are colocalized in primary afferent sensory fibers in rat urinary bladder, the receptors for these neuropeptides are located on different cell types and may be subject to different neural influences.