Role of nitric oxide in mediating non-adrenergic non-cholinergic relaxation of the cat ileocecal sphincter

Abstract

The participation of nitric oxide (NO) in field stimulation- or nicotine-evoked non-adrenergic non-cholinergic (NANC) relaxation of cat ileocecal sphincter was studied in vitro. During a 30 microM noradrenaline-induced contraction, both the application of electrical field stimulation (2-20 Hz, 0.2 ms, supramaximal current intensity, 10 s duration) and (-)-nicotine (10-500 microM) produced a tetrodotoxin-sensitive relaxation. The maximal relaxation was observed at 10 Hz or 100 microM (-)-nicotine. In 12 out of 19 strips the pretreatment with N omega-nitro-L-arginine (100 microM) decreased the amplitude of the field stimulation-evoked relaxation, while in the remaining strips the relaxation was transformed into a contraction. By increasing the concentration of N omega-nitro-L-arginine up to 1 mM all strips responded to field stimulation with a frequency-dependent tetrodotoxin-resistant contraction. N omega-Nitro-L-arginine (100 microM) completely inhibited the nicotine-induced relaxation. L-Arginine (1 mM) restored the amplitude of both field stimulation- and nicotine-evoked relaxations. These data indicate that NO appears to be involved in both field stimulation- and nicotine-evoked NANC relaxations. Evidence has been obtained for the existence of tetrodotoxin-resistant NANC contraction in cat ileocecal sphincter.