CAPSAICIN AND BRADYKININ-INDUCED SUBSTANCE-P-ERGIC RESPONSES IN THE IRIS SPHINCTER MUSCLE OF THE RABBIT

  • 1 January 1984
    • journal article
    • research article
    • Vol. 230  (2) , 469-473
Abstract
Exogenously applied capsaicin and bradykinin produced contractile responses in the rabbit iris sphincter muscle. Responses were suppressed remarkably by [D-Pro2, D-Trp7,9]-substance P, a substance P antagonist, and disappeared in trigeminally denervated preparations. Thus, the responses to capsaicin or bradykinin were considered to be mediated by substance P released from the trigeminal nerve. Repetitive application of capsaicin or bradykinin produced a gradual decline in the responses, thereby indicating the tachyphylaxis development. Furthermore, bradykinin failed to induce any response after the development of capsaicin-induced tachyphylaxis, but after the development of tachyphylaxis to bradykinin, responses to capsaicin persisted. Electrical transmural stimulation produced cholinergic and substance P-ergic responses in the rabbit iris sphincter muscle. Substance P-ergic response to electrical transmural stimulation also was abolished after development of tachyphylaxis to capsaicin, but not to bradykinin. The contractile response to exogenously applied substance P was unaffected by the development of tachyphylaxis to capsaicin and bradykinin. Capsaicin and bradykinin apparently produce substance P-ergic contractile responses mediated by the trigeminal nerve; the mechanisms of action differ between the 2 drugs. Capsaicin and bradykinin effects are discussed in relation to occurrence of neurogenic inflammation in the eye.

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