Answer: The neurotransmitters that stimulate GI smooth muscle contractions include acetylcholine (ACh) and other muscarinic agonists which act via muscarinic receptors.
Explanation: The muscarinic receptors play a key role in the parasympathetic nervous control of various peripheral tissues including smooth muscles1. In addition, adrenaline and noradrenaline are ligands to α1, α2, or β-adrenergic receptors. α1-receptors couple to Gq, resulting in increased intracellular Ca2+ and causing smooth muscle contraction. α2 receptors couple to Gi, causing a decrease in cAMP activity and resulting in smooth muscle contraction. β-receptors couple to Gs, increasing cAMP activity and resulting in smooth muscle relaxation.
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