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Twenty-Four-Hour Profile of Plasma Glucose and Glucoregulatory Hormones during Normal Living Conditions in Trained and Untrained Men^*

Department of Medical Physiology B, The Panum Institute, University of Copenhagen, University Hospital Copenhagen, Denmark
Department of Urology and Endocrine Surgery D, 2111, University Hospital Copenhagen, Denmark
Department of Internal Medicine TTA, 2001, University Hospital Copenhagen, Denmark

Address all correspondence and requests for reprints to: Flemming Dela, M.D., Department of Medical Physiology B, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen N Denmark.

Compared with untrained (UT) subjects, in trained (T) subjects the increased insulin sensitivity and decreased glucose induced insulin secretion would tend to promote health by decreasing glucose levels and insulin secretion whereas the increased food intake would tend to increase these variables. To study the net effect of training, blood was sampled from seven T and eight UT young men [: 76 ± 2 (T) vs. 48 % 1 (UT) mL • kg^–1 • min^–1’ for 24 h during ordinary living conditions. Athletes exercised 204 % 20 min and ate 50% more calories and 130% more carbohydrate than UT subjects (P < 0.05). However, 24-h integrated plasma concentrations of glucose, C-peptide, glucagon, free fatty acids, and glycerol as well as glycosylated hemoglobin levels were identical in T and UT subjects. Mean insulin concentration was 41% lower in T than in UT but levels differed significantly (P < 0.05) only late during the night. Urinary excretion of pancreatic peptides paralleled plasma concentrations. In conclusion, during training adaptations in pancreas- and insulin-sensitive tissues allow the necessary increase in food intake without harmful hyperglycemia and overloading of β-cells, but sparing of insulin secretion and reductions in glucose levels are only relative to food intake. However, training may be wholesome by increasing hepatic insulin extraction and thereby decreasing arterial insulin levels. Training-induced β-cell adaptation is not caused by diminished average glucose levels. Finally, renal handling of insulin, C-peptide, and glucagon is not influenced by training.

^* The financial support from The Danish Diabetes Association, The Danish Foundation for the Advancement of Medical Science, The Danish Sports Research Council (J.nr. 87–2–03 and 88–2–02), Jacob and Olga Madsens Foundation, The NOVO Foundation, The P. Carl Petersen Foundation (J.nr. B.45), and The Danish Medical Research Council (J.nr. SLF-12–8172 and SSVF-12–9360) is gratefully acknowledged.

Received December 19, 1990.

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