Effects of the Menstrual Cycle on Resting Muscle Glycogen Content A. C. Hackney Exercise Physiology Laboratory, University of North Carolina, Chapel Hill, North Carolina, U . S . A .
Reent preliminary evidence indicates that muscle glycogen content and synthesis rates in eumenorrheic women may vary with dietary practices and the phases of the menstrual cycle {Nicklas, Hackney and Sharp 1989). The physiological basis for this effect was proposed to be the endogenous fluctuations in the ovarian steroid hormones (i. e., estrogens and progesterone). Such a hypothesis is consistent with the existing animal based research (Matute and Kalkhoff 1973; Sladek 1974). The intent of this study was to examine this issue in humans, and determine if the resting muscle glycogen content of eumenorrheic women was different at the mid-follicular and mid-luteal phases of the menstrual cycle.
Methods Ten healthy young adult females gave informed consent to participate in this study. Their physical characteristics were as follows: age =25.0 ±1.6 yrs, weight 57.6 + 2.4 kg and height 165.5 + 2.0 cm (X + SEM). The subjects were asked to keep daily basal body temperature records for approximately 2 - 3 months in order to determine ovulation (+ 0.3 °C increase in temperature), and thus allow for cycle phases to be determined. Additionally, many of the subjects (n = 6) had previously participated in extensive hormonal profiling studies. These profile records were also used to determine cycle phases. The subjects were found to have average cycle lengths of 29.5 ± 1.0 days. None of the subjects were on oral contraceptives at the time of the study or had reported any menstrual irregularities for the previous 6—8 months.
Results and Discussion A total of thirteen muscle samples were obtained at each of the mid-follicular and mid-luteal trials. The statistical analysis indicated that the mid-follicular muscle glycogen content (90.76 + 3.56 umol/g w. w.) was significantly less than the mid-luteal content (102.05 + 4.97 umol/g w. w.). These findings agree with animal based research which has examined the effects of natural, as well as manipulated, estrous cycles on hepatic and muscle glycogen content (Mature and Kalkhoff 1973; Sladek 1974). Furthermore, previous work with humans from our laboratory has shown glycogen content/storage rates vary during the menstrual cycle if a diet high in carbohydrate is consumed (Nicklas, Hackney and Sharp 1989). The present results suggest that resting glycogen content differs throughout the menstrual cycle with even a normal mixed diet. The physiological implications of these findings remain to be determined. However, the results do have several pragmatic connotations. First, human metabolic studies where muscle glycogen is an experimental variable should consider the effects of the menstrual cycle if women are to be used as subjects. Secondly, muscle glycogen content is known to directly effect endurance exercise capacity (Costill and Miller 1980). Therefore, eumenorrheic women endurance athletes have the potential to experience reduced muscle glycogen at the mid-follicular point of their menstrual cycle which may subsequently influence their exercise ability. References
Muscle needle biopsies were performed on the vastus lateralis (10—15 cm proximal to the patella) of the dominant leg at the mid-follicular (cycle day 8± 1) and mid-luteal (cycle day 2 2 + 1 ) phases of the menstrual cycle. Diet, physical activity, and sexual activity were controlled and replicated for the 36 hours prior to each biopsy. The order of biopsies (follicular vs. luteal) was randomized, but consecutive. Additionally, three subjects had the entire procedure performed twice. Extracted muscle tissue was rapidly cleaned of blood, then frozen in isopentane cooled to its freezing point by liquid nitrogen. Tissue samples were divided into ~ 8 —10 mg aliquots and stored at - 80 °C for later analysis. Glycogen content analysis was performed on HC1 and heat treated tissue extracts as described by Lowry and Passoneau (1974). All determinations were performed in duplicate. Statistical analysis of the data was performed with a two-tailed dependent t-test with significance set at P < 0.05.
Horm. metab. Res. 22 (1990) 647 © Georg Thieme Verlag Stuttgart • New York
Costill, D. L., J. Miller: International Journal of Sports Medicine 1:2— 14(1980) Lowry, O. H., J. V, Passoneau: A flexible system of enzymatic analysis. Academic Press, New York (1974) Matute, M. L., R. K. Kalkhoff: Endocrinology 92: 762-768 (1973) Nicklas, B. J., A. C. Hackney, R. L. Sharp: International Journal of SportMedicine 10:264-269(1989) Sladek, C. D..Hormone and Metabolic Research 6:217-221 (1974)
Requests for reprints should be addressed to: Dr. A. C, Hackney Exercise Physiology Laboratory Department of Exercise & Sport Science University of North Carolina Chapel Hill, North Carolina 27599-8700 (U. S. A.)
Received: 27 June 1990
Accepted: 10 Aug. 1990
Downloaded by: University of Pennsylvania Libraries. Copyrighted material.
Introduction
Reent preliminary evidence indicates that muscle glycogen content and synthesis rates in eumenorrheic women may vary with dietary practices and the phases of the menstrual cycle {Nicklas, Hackney and Sharp 1989). The physiological basis for this effect was proposed to be the endogenous fluctuations in the ovarian steroid hormones (i. e., estrogens and progesterone). Such a hypothesis is consistent with the existing animal based research (Matute and Kalkhoff 1973; Sladek 1974). The intent of this study was to examine this issue in humans, and determine if the resting muscle glycogen content of eumenorrheic women was different at the mid-follicular and mid-luteal phases of the menstrual cycle.
Methods Ten healthy young adult females gave informed consent to participate in this study. Their physical characteristics were as follows: age =25.0 ±1.6 yrs, weight 57.6 + 2.4 kg and height 165.5 + 2.0 cm (X + SEM). The subjects were asked to keep daily basal body temperature records for approximately 2 - 3 months in order to determine ovulation (+ 0.3 °C increase in temperature), and thus allow for cycle phases to be determined. Additionally, many of the subjects (n = 6) had previously participated in extensive hormonal profiling studies. These profile records were also used to determine cycle phases. The subjects were found to have average cycle lengths of 29.5 ± 1.0 days. None of the subjects were on oral contraceptives at the time of the study or had reported any menstrual irregularities for the previous 6—8 months.
Results and Discussion A total of thirteen muscle samples were obtained at each of the mid-follicular and mid-luteal trials. The statistical analysis indicated that the mid-follicular muscle glycogen content (90.76 + 3.56 umol/g w. w.) was significantly less than the mid-luteal content (102.05 + 4.97 umol/g w. w.). These findings agree with animal based research which has examined the effects of natural, as well as manipulated, estrous cycles on hepatic and muscle glycogen content (Mature and Kalkhoff 1973; Sladek 1974). Furthermore, previous work with humans from our laboratory has shown glycogen content/storage rates vary during the menstrual cycle if a diet high in carbohydrate is consumed (Nicklas, Hackney and Sharp 1989). The present results suggest that resting glycogen content differs throughout the menstrual cycle with even a normal mixed diet. The physiological implications of these findings remain to be determined. However, the results do have several pragmatic connotations. First, human metabolic studies where muscle glycogen is an experimental variable should consider the effects of the menstrual cycle if women are to be used as subjects. Secondly, muscle glycogen content is known to directly effect endurance exercise capacity (Costill and Miller 1980). Therefore, eumenorrheic women endurance athletes have the potential to experience reduced muscle glycogen at the mid-follicular point of their menstrual cycle which may subsequently influence their exercise ability. References
Muscle needle biopsies were performed on the vastus lateralis (10—15 cm proximal to the patella) of the dominant leg at the mid-follicular (cycle day 8± 1) and mid-luteal (cycle day 2 2 + 1 ) phases of the menstrual cycle. Diet, physical activity, and sexual activity were controlled and replicated for the 36 hours prior to each biopsy. The order of biopsies (follicular vs. luteal) was randomized, but consecutive. Additionally, three subjects had the entire procedure performed twice. Extracted muscle tissue was rapidly cleaned of blood, then frozen in isopentane cooled to its freezing point by liquid nitrogen. Tissue samples were divided into ~ 8 —10 mg aliquots and stored at - 80 °C for later analysis. Glycogen content analysis was performed on HC1 and heat treated tissue extracts as described by Lowry and Passoneau (1974). All determinations were performed in duplicate. Statistical analysis of the data was performed with a two-tailed dependent t-test with significance set at P < 0.05.
Horm. metab. Res. 22 (1990) 647 © Georg Thieme Verlag Stuttgart • New York
Costill, D. L., J. Miller: International Journal of Sports Medicine 1:2— 14(1980) Lowry, O. H., J. V, Passoneau: A flexible system of enzymatic analysis. Academic Press, New York (1974) Matute, M. L., R. K. Kalkhoff: Endocrinology 92: 762-768 (1973) Nicklas, B. J., A. C. Hackney, R. L. Sharp: International Journal of SportMedicine 10:264-269(1989) Sladek, C. D..Hormone and Metabolic Research 6:217-221 (1974)
Requests for reprints should be addressed to: Dr. A. C, Hackney Exercise Physiology Laboratory Department of Exercise & Sport Science University of North Carolina Chapel Hill, North Carolina 27599-8700 (U. S. A.)
Received: 27 June 1990
Accepted: 10 Aug. 1990
Downloaded by: University of Pennsylvania Libraries. Copyrighted material.
Introduction
