Which of the following statements best explains the action of nitroglycerine on coronary vessels:: (A) It mitigates angina pectoris by increasing total coronary flow, (B) It preferentially dilates conducting aeries without affecting resistance aerioles, (C) It preferentially dilates autoregulatory aerioles without affecting the larger aeries, (D) It mainly decreases the after load
Answer is B. Nitrates cause redistribution of blood flow without affecting total coronary flow. Autoregulatory small vessels remain unaffected whereas large conducting vessels are dilated. Nitrates are predominantly venodilators, therefore decrease mainly preload.