Capsazocaine: a capsaicin-sensitive functional antagonist displays an argument on sensory capsaicin receptor

1. Intravenous infusion of capsazocaine (CAPBZ), a molecular fusion product of irritant synthetic capsaicin and local analgesic benzocaine, at 100 micrograms/kg/min for 15 min inhibited capsaicin (10 micrograms/kg, IV)-induced spinal release of substance P-like immunoreactivity and vagus reflex responses in blood pressure and heart rate changes in rats. 2. Intrathecal perfusion of CAPBZ (1.0 nM) also reversed retrograde epigastric intraarterial capsaicin (10 micrograms/kg)-induced hypotensive spinal reflex. 3. In isolated guinea pig tissues, CAPBZ (1.0-100.0 microM) inhibited capsaicin (1.0 microM)-sensitive sensory and functional activities, including cardiatonic, bronchial, tracheal and ileal contractilities. CAPBZ is suggested to be a capsaicin antagonist.