No effect of menstrual cycle on myofibrillar and connective tissue protein synthesis in contracting skeletal muscle

1 Institute of Sports Medicine, Copenhagen, Bispebjerg Hospital, Copenhagen; 2 Department of Endocrinology, Aarhus University Hospital, Aarhus; 3 Osteoporosis and Metabolic Bone Unit, Department of Clinical Biochemistry, Copenhagen University Hospitals, Hvidovre, Denmark; 4 Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dundee, Scotland; and 5 University of Nottingham, Graduate Medical School, Derby City General Hospital, Derby, England, United Kingdom Submitted 4 July 2005 ; accepted in final form 29 August 2005 We tested the hypothesis that acute exercise would stimulate synthesis of myofibrillar protein and intramuscular collagen in women and that the phase of the menstrual cycle at which the exercise took place would influence the extent of the change. Fifteen young, healthy female subjects were studied in the follicular (FP, n = 8) or the luteal phase (LP, n = 7, n = 1 out of phase) 24 h after an acute bout of one-legged exercise (60 min of kicking at 67% W max ), samples being taken from the vastus lateralis in both the exercised and resting legs. Rates of synthesis of myofibrillar and muscle collagen proteins were measured by incorporation of [ 13 C]leucine. Myofibrillar protein synthesis (means ± SD; rest FP: 0.053 ± 0.009%/h, LP: 0.055 ± 0.013%/h) was increased at 24-h postexercise (FP: 0.131 ± 0.018%/h, P < 0.05, LP: 0.134 ± 0.018%/h, P < 0.05) with no differences between phases. Similarly, muscle collagen synthesis (rest FP: 0.024 ± 0.017%/h, LP: 0.021 ± 0.006%/h) was elevated at 24-h postexercise (FP: 0.073 ± 0.016%/h, P < 0.05, LP: 0.072 ± 0.015%/h, P < 0.05), but the responses did not differ between menstrual phases. Therefore, there is no effect of menstrual cycle phase, at rest or in response to an acute bout of exercise, on myofibrillar protein synthesis and muscle collagen synthesis in women. stable isotopes; estrogen; exercise Address for reprint requests and other correspondence: B. Miller, Skeletal Muscle Adaptation Laboratory, Dept. of Sport and Exercise Science, Univ. of Auckland, Private Bag 92019, Auckland, New Zealand (e-mail: b.miller{at}auckland.ac.nz )