<prompt> The primary action of Nitric oxide NO in the gastrointestinal tract isVasodilatationVasoconstrictionGastrointestinal smooth muscle relaxationGastrointestinal slow smooth muscle contraction  <response>: In the gastrointestinal tract,NO impoant in the relaxation of smooth muscle NO act as inhibitory neurotransmitter in git. It doesnt have membrane bound receptor and diffuses into target cells and iactivates guanyl cyclase- produces cGMP from GTP- mediates smooty muscles relaxation. 