<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:An investigator is studying brachial artery reactivity in women with suspected coronary heart disease. The brachial artery diameter is measured via ultrasound before and after intra-arterial injection of acetylcholine. An increase of 7 in the vascular diameter is noted. The release of which of the following is most likely responsible for the observed effect?? A: Nitric oxide from endothelial cells, B: Endothelin from the peripheral vasculature, C: Serotonin from neuroendocrine cells, D: Norepinephrine from the adrenal medulla, E: Atrial natriuretic peptide from atrial myocytes,  <response>: This is a question about brachial artery reactivity testing. The question describes an experiment where brachial artery diameter was measured before and after injection of acetylcholine. There was an increase in diameter, indicating vasodilation occurred. The choices describe different vasoactive substances. Based on the vasodilation seen with acetylcholine, the substance responsible is most likely nitric oxide. Acetylcholine stimulates nitric oxide release from endothelial cells, causing vasodilation. Endothelin and norepinephrine cause vasoconstriction rather than vasodilation. Serotonin and ANP may play a role in vascular regulation but are not directly stimulated by acetylcholine.A: Nitric oxide from endothelial cells 