Study 1: Dose-response study Sufficient volunteers will be recruited to complete 8 studies using an incremental rising dose infusion of intra-arterial NAC (6 doses) to determine a dose response curve for arterial vasodilatation in the forearm. After a washout period of 30 mins to ensure a return to normal state, this will be repeated to determine whether the response is consistent over time. Study 1 will identify a dose to be used in study 2 that causes maximum local forearm vasodilatation without systemic effects (rise in contralateral forearm blood flow, blood pressure, heart rate, facial flushing).