title: 13C/31P NMR studies on the role of glucose transport/phosphorylation in human glycogen supercompensation.
abstract: This study measured muscle glycogen during a 7-day carbohydrate loading protocol. Twenty healthy subjects (12 male, 8 female) performed 1 hr treadmill/toe-raise exercise immediately before a 3-day low carbohydrate (LoCHO) diet (20 % carbohydrate, 60 % fat, 20 % protein). On day 3 they repeated the exercise and began a 4-day high carbohydrate (HiCHO) diet (90 % carbohydrate, 2 % fat, 8 % protein). The order of administration of the diet was reversed in a subpopulation (n = 3). Interleaved natural abundance 13C/ 31P NMR spectra were obtained before and immediately after exercise, and each day during the controlled diets in order to determine concentrations of glycogen (GLY), glucose-6-phosphate (G6P), and muscle pH. Following exercise, muscle GLY and pH were reduced (p < 0.001) while muscle G6P was elevated (p </= 0.01). During the 3-day LoCHO diet, fasting concentrations of G6P were not different from resting levels. During the first 3 days of the HiCHO diet, resting G6P was elevated (p </= 0.05) compared to before the study. By the final day, muscle glycogen was 1.6-fold greater than before the protocol, while G6P had returned to baseline. Daily GLY and G6P were not affected by the order in which the diet was administered. We conclude that increased glucose transport/phosphorylation plays a role in muscle glycogen supercompensation.
authors.affiliation: Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT 06510, USA. thomas.price@yale.edu
authors.forename: T B
authors.initials: TB
authors.lastname: Price
authors.forename: D
authors.initials: D
authors.lastname: Laurent
authors.forename: K F
authors.initials: KF
authors.lastname: Petersen
mesh_terms: D000328:Adult; D001692:Biological Transport / Q000502:physiology; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D015444:Exercise / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000378:metabolism*; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010766:Phosphorylation; D013995:Time
chemical_list: D004040:Dietary Carbohydrates; D019298:Glucose-6-Phosphate; D006003:Glycogen; D005947:Glucose