ADMINISTRATION OF ORAL ACETYLCYSTEINE/PLACEBO Participants will receive 3 blister packs of acetylcysteine or placebo capsules and be asked to take the appropriate capsules at 08.00 and 20.00 on the day before the study day (Day 1; Day 2 being the day spent in the CRF). They will also be asked to drink an extra 500ml of water to ensure adequate hydration. Hard capsules containing acetylcysteine 600 mg or matched placebo (Lactose PhEur 600 mg) will be prepared by Tayside Pharmaceuticals, Dundee, and packaged in patient packs of 8 capsules. The capsules will be delivered to the hospital pharmacy and supplied to participants according to the randomized allocation order.