Autoradiographic localization of substance P binding sites in rat footpad skin.

The autoradiographic distribution of binding sites for 60 pM [125I]Bolton-Hunter substance P (BHSP) was investigated in slide-mounted sections of rat footpad skin. BHSP binding sites were found over dermal papillae, postcapillary venules, sweat glands and arterioles. No binding was seen over mast cells, sebaceous glands or pacinian corpuscles. Specific BHSP binding was inhibited by substance P greater than neurokinin A greater than neurokinin B, indicating binding to an NK1 (substance P-preferring) site. The NK1 binding sites over postcapillary venules and arterioles probably represent receptors mediating plasma extravasation and vasodilatation, respectively. There was no apparent change in distribution or number of BHSP binding sites after neonatal capsaicin pretreatment, indicating a probable absence of NK1 receptors on sensory terminals. No binding sites were observed for 100 pM [125I]iodohistidyl neurokinin A (INKA).