A COMPARISON OF THE EFFECTS OF CAPSAICIN WITH INHIBITORY NERVE-STIMULATION IN THE RAT ANOCOCCYGEUS MUSCLE IN-VITRO

Capsaicin was used to test whether centrifugal activation of sensory f ibres in the rat anococcygeus muscle can contribute to non-adrenergic non-cholinergic (NANC) relaxation of the muscle. In a solution contain ing 0.5 mM Ca2+ and in the presence of carbachol (10 mu M) capsaicin e voked a fast concentration-dependent relaxation of the muscle that was usually followed by a smaller, slower, relaxant response. The fast re laxant response was reduced when extracellular Ca2+ was raised to 2.5 mM, desensitized after a single application of capsaicin and was block ed by tetrodotoxin (1 mu M) or ruthenium red (10 mu M) The fast respon se was greatly reduced by haemoglobin, by cold storage of the muscles or by N-monomethyl-L-arginine (100 mu M) in the absence but not in the presence of L-arginine (100 mu M) It is concluded that centrifugal ac tivation of sensory fibres evokes a nitric oxide-mediated relaxation o f the anococcygeus muscles that probably contributes to electrically e voked NANC relaxation. (C) 1998 Elsevier Science B.V. All rights reser ved.