Prostaglandins enhance trigeminal substance P-ergic responses in the rabbit iris sphincter muscles

Contractile responses due to substance P released from the trigeminal nerve were observed after electrical transmural stimulation or exogenous application of bradykinin in the isolated rabbit iris sphincter muscle. Prostaglandins, particulary prostaglandin E1, enhanced and indomethacin inhibited these substance P-ergic responses. Since the responses to exogenously applied substance P were neither affected by prostaglandins nor indomethacin, it was suggested that prostaglandins acted presynaptically to enhance the release of substance P from the trigeminal nerve terminals.