This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Mediator present in mast cells is \nSelect and explain. \nA. Histamine, B. Encephalin, C. Calmodulin, D. None of these', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Mast cells release several different substances. Among them areHistamineSlow-reacting substance of anaphylaxis (which is a mixture of leukotrienes)Eosinophilic chemotactic factorBradykininRef: Guyton and Hall textbook of medical physiology 13th edition. Page:554', 'role': 'assistant'}]