ROLE OF NITRIC-OXIDE IN MEDIATING NONADRENERGIC NONCHOLINERGIC RELAXATION OF THE CAT ILEOCECAL SPHINCTER

The participation of nitric oxide (NO) in field stimulation- or nicoti ne-evoked non-adrenergic non-cholinergic (NANC) relaxation of cat ileo cecal sphincter was studied in vitro. During a 30 mu M noradrenaline-i nduced contraction, both the application of electrical field stimulati on (2-20 Hz, 0.2 ms, supramaximal current intensity, 10 s duration) an d (-)-nicotine (10-500 mu M) produced a tetrodotoxin-sensitive relaxat ion. The maximal relaxation was observed at 10 Hz or 100 mu M (-)-nico tine. In 12 out of 19 strips the pretreatment with N-omega-nitro-L-arg inine (100 mu M) decreased the amplitude of the field stimulation-evok ed relaxation, while in the remaining strips the relaxation was transf ormed into a contraction. By increasing the concentration of N omega-n itro-L-arginine up to 1 mM all strips responded to field stimulation w ith a frequency-dependent tetrodotoxin-resistant contraction. N-omega- Nitro-L-arginine (100 mu M) completely inhibited the nicotine-induced relaxation. L-Arginine (1 mM) restored the amplitude of both field sti mulation- 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 tet rodotoxin-resistant NANC contraction in cat ileocecal sphincter.