1. Department of Clinical and Surgical Sciences (Surgery), The University of Edinburgh, Royal Infirmary, Edinburgh EH16 4SA, Scotland, U.K.
2. Isotope Biochemistry Laboratory, Scottish Universities Environmental Research Centre, East Kilbride G75 0QF, Scotland, U.K.
3. Department of Surgery, Glasgow Royal Infirmary, Glasgow G31 2ER, Scotland, U.K.
4. Division of Developmental Medicine, University of Glasgow, Yorkhill Hospitals, Glasgow G3 8SJ, Scotland, U.K.