Mechanism mediating nitric oxide - Induced inhibition in human jejunal longitudinal smooth muscle

Background. Enteric neurotransmission is a complex process involving multiple neurotransmitters, including nitric oxide (NO). Our aim was to evaluate the role and mechanism(s) of action of NO in normal human jejunal longitudinal smooth muscle. Methods. Transmural strips of normal human jejunum obtained from subjects undergoing gastric bypass were studied in organ chambers. Effects of exogenous NO (7 × 10^-6 mol/L to 7 × 10^-5 mol/L) and electrical field stimulation (nonspecific release of endogenous neurotransmitters) on spontaneous contractile activity and on precontracted muscle strips (substance P, 10^-5 mol/L) were evaluated in the presence and absence of the competitive NO synthase inhibitor N^G-amino-L-arginine (L-NNA, 10^-3 mol/L) and the specific soluble guanylyl cyclase inhibitor 1H-[1,2,4]-oxadiazaolo-[4,3-a]-quinoxalin-1-one (ODQ 10^-5 mol/L and 10^-4 mol/L). Results. Exogenous NO dose-dependently inhibited spontaneous contractility and relaxed precontracted smooth muscle strips. The effects of NO were markedly attenuated or completely inhibited in the presence of ODQ. Electric field stimulation under nonadrenergic, noncholinergic conditions also inhibited spontaneous contractility and relaxed precontracted smooth muscle strips; both of these effects were attenuated, but not completely inhibited, in the presence of both ODQ and L-NNA. Conclusions. NO is an endogenous inhibitory neurotransmitter in human jejunal longitudinal smooth muscle, acting at least in part via a mechanism mediated by guanylyl cyclase. Other (non-nitrergic) nonadrenergic, noncholinergic inhibitory neurotransmitters are likely active in this portion of the human gut.