This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sympathetic System, Subject name: Pharmacology
[{'content': 'Which of the following effects of adrenaline would be blocked by phentolamine but NOT by propanolol? \nSelect and explain. \nA. Cardiac stimulation, B. Relaxation of bronchial smooth muscle, C. Relaxation of the uterus, D. Contraction of the radial smooth muscle in the iris', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Phentolamine is an a blocker whereas propranolol is a b blocker. So, phentolamine will block those actions which are mediated by a receptors .i.e. contraction of radial smooth muscle in the iris.', 'role': 'assistant'}]