Physiology The primary action of the neurotransmitter Nitric oxide (NO) in the gastrointestinal tract is: A Vasodilatation B Vasoconstriction C Gastrointestinal smooth muscle relaxation D Gastrointestinal slow smooth muscle contraction 💡 Explanation The primary action of the neurotransmitter Nitric oxide (NO) in the gastrointestinal tract is: ✓ Correct Answer: C. Gastrointestinal smooth muscle relaxation