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The Effect of Reproductive Hormones on Muscle Function in Young and Middle-Aged Females

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The Effect of Reproductive Hormones on Muscle Function in Young and Middle-Aged Females THE EFFECT OF REPRODUCTIVE HORMONES ON MUSCLE FUNCTION IN YOUNG AND MIDDLE-AGED FEMALES JULIE GREEVES A thesis submitted in partial fulfilment of the requirements of Liverpool John Moores University for the degree of Doctor of Philosophy May 1997 PAGE NUMBERING A ORIGIN L THE FOLLOWING MATERIAL HAS NOT BEEN DIGITISED AT THE REQUESTOF THE AWARDING UNIVERSITY; PAGE 7 FIG 2.1.1 PAGE 8 FIG 2.1.2 PAGE 13 FIG 2.1.4 PAGE 14 FIG 2.1.5 PAGE 15 FIG 2.1.7 PAGE 17 FIG 2.1.8 PAGE 24 FIG 2.1.12 PAGE 27 FIG 2.1.13 PAGE 28 FIG 2.1.14 PAGE 29 TABLE 2.1.3 PAGE 36 FIG 2.1.17 PAGE 40 FIG 2.1.18 CHAPTER 4.3 PAGE 173-182 APP 4 PAGE 173-182 ABSTRACT The menopause is associated with a deficiency of reproductive hormones, and accompanied by a significant loss of bone mass. This bone loss is accelerated within the first five years post-menopause. Muscle strength at this time would have important clinical implications for correcting imbalance and preventing falls. The aim of the studies within this thesis were to 1) determine the rate and time course of force loss of the quadriceps muscle group over 12 months in three groups of women with varying hormonal status 2) establish the role of oestrogen in this weakness and 3) investigate the effectiveness of hormone replacement therapy (HRT) in maintaining muscle function. The reliability of an isokinetic dynamometer and a strain gauge assembly was examined initially to determine the inherent variability of muscle function assessment. Strength of the knee extensors measured on the isokinetic dynamometer was deemed reliable in middle-aged women, although at 1.05 rad/s more practice trials were needed to attain peak torque. Measurements of the knee flexors were highly variable. Maximal voluntary isometric contractions were repeatable using the strain gauge system, for both the knee extensors and first dorsal interosseus (FOI) muscle. There was greater variability in force production generated from electrically stimulated contractions. Maximal strength of the knee extensors declined by 9.3±4.6 and I0.3±3.1% (mean±SE) for dynamic (1.05 radls) and isometric strength respectively over 9 months in hypoestrogenic post-menopausal women. There were no changes at higher angular velocities, or for handgrip strength. These results support the role of reproductive hormones in influencing force production, which is further endorsed by the observation that females on HRT did not experience a reduction in strength over this time. The force loss was significant only when the post-menopausal and HRT group were compared (p<0.05). The post- menopausal group were within I to 3 years past the menopause, the time period in which bone loss is rapid. This rapid loss of strength would therefore be expected to level out, similarly to bone. The menopause is an oestrogen-deficient and progesterone-deficient endocrinopathy. It is not possible to identify which hormone, if not both, is responsible for these observed changes in strength. To explore the relationship between acute changes in oestrogen and progesterone and strength, maximal force production of the quadriceps and first dorsal interosseus (FOI) was measured across the menstrual cycle. Maximal strength of the quadriceps was lowest prior to the surge in luteinizing hormone (LH) and reached its peak mid-luteal, a difference of 12.6±4.3% (mean±SE). These changes were significantly different (p<O.OS). From these results, there does not appear to be a role of unopposed oestrogen influencing force production but the pattern of strength changes implicates progesterone. There were no corresponding fluctuations in strength of the FOI, which remained relatively stable across the menstrual cycle. The contractility and fatigue resistance of the quadriceps did not differ significantly between any phase (p>O.OS).The difficulty in isolating oestrogen during the menstrual cycle does not render this a good model to assess its effects upon force production. Maximal strength and fatiguability of the FDI were examined in young women undergoing in vitro fertilisation (IVF) treatment when acute, massive changes in oestrogen are induced. There were no differences in muscle function of the FDI when assessed under very low or high oestrogen changes (p>O.05). The independent effects of oestrogen upon muscle function were not demonstrated here. Hormone replacement therapy is the most efficacious treatment for preventing menopausally-related bone loss. The results from the longitudinal study suggest that HRT confers protection against muscle weakness as a consequence of ovarian failure. Whether HRT maintains or restores strength was examined in the FDI of post-menopausal women (n=9). The oestrogen only and oestrogen-progestogen phases were compared with baseline measurements. A positive change in strength was observed, although this did not reach significance (p<O.1). The increase in strength (15.2±20.6%) between baseline and the oestrogen-progestogen phase of HRT corroborates the involvement of progesterone in determining muscle function. The findings suggest that the menopause is associated with a loss of strength, prevented by the administration of HRT. Oestrogen alone does not influence force production, although progesterone is impli~!ed. This has important ramifications in hysterectomised women who are prescribed preparations contammg oestrogen only. 1 ACKNOWLEDGEMENTS I extend my sincere gratitude to Dr. N.T. Cable and Prof. Tom Reilly for their guidance and advice during the supervision of my PhD. I would also like to express a special thanks to Dr. Tim Cable whose continued support, motivation and understanding during the experimental work and writing up of this thesis has been appreciated. Much of the work within this thesis was undertaken in collaboration with The Women's Hospital, Liverpool. Without the cooperation of staff at the Reproductive Medicine Unit, this would not have been possible. I would like to thank Mr Charles Kingsland for allowing access to his patients, Dr. M. Biljan for his enthusiasm and ideas and for the help of Dr. M. Luckas, who was involved with three of the studies within this thesis (studies 4.2, 4.3,4.4). The assistance of Dr. G. Atkinson and Dr. A. Nevill with the statistical analyses is gratefullyackowledged. I would like to thank Una Creagh, Diana Leighton, Barry Drust and Lee Nolan for their friendshipand the support and encouragement they have offered. I hope this will continue. I would finallylike to acknowledge my parents for their love and support throughout my life and their belief in my abilities. My sister, Lynda, for her constant source of encouragement. To Simon, for his patience, love and constant faith in me. Without this support from my familyI would never have reached this far. I therefore dedicate this thesis to them 11 LIST OF CONTENTS Abstract t Acknowledgements ii List of Contents iii List of Figures x List ofTables xiv List of Plates xv Ethics Approval xvi 1.1. Introduction 1 1.2. Aims and objectives 3 2.0. REVIEW OF THE LITERA TURE 5 2.1. Theorectical background of the human reproductive system From menarche to menopause 5 2.1.1. Endocrinology of the human female menstrual cycle 5 2.1.1.1. Structure and function of the ovary 6 2.1.1.1.2. Morphology of the ovary and follicular development. 6 2.1.1.2. Hypothalamic 'neural' and pituitary control.. 8 2.1.1.3. Ovarian control 9 2.1.1.4. Follicular (proliferative) phase l0 2.1.1.5. Mid-cycle dynamics l1 2.1.2. Biosynthesis of reproductive steroid hormones 14 2.1.3. Oral contraceptives 18 2.1.4. The menopause and climacteric 21 2.1.4.1. Epidemiology of the menopause 21 2.1.4.2. Aetiology of the menopause 23 2.1.5. Endocrinolgy of the menopause 24 2.1.5.1. Endocrine changes before the menopause 25 2.1.5.2. Endocrine changes at the menopause 26 2.1.5.3. Endocrine changes after the menopause 27 ... ill 2.1.6. Physiological and pathological changes 29 2.1.6.1. Acute responses (vasomotor symptoms) .30 2.1.6.2. Intermediate responses 31 2.1.6.3. Chronic responses 31 2.1.6.3.1. Cardiovascular disease 32 2.1.6.3.2. Skeletal changes 34 2.1.7. Hormone replacement therapy .40 2.1.7.1. Formulation 41 2.1.7.2. Route ofadministration 42 2.2. Muscle function 43 2.2.1. Introduction. 43 2.2.2. Structure of skeletal muscle 44 2.2.3. Excitation-contraction coupling .47 2.2.3.1. Cross-bridge cycling 47 2.2.4. Force-velocity relations 48 2.2.5. Assessment of muscle function 50 2.2.5.1. Maximal voluntary muscle force 50 2.2.5.2. Electrical stimulation 52 2.2.6. Muscle weakness 53 2.2.7. Muscle fatigue 54 2.2.7.1. Central fatigue 55 2.2.7.2. Peripheral fatigue 56 2.2.7.2.1. Metabolic causes offatigue 56 2.2.7.2.2. High frequency fatigue 58 2.2.7.2.3. Low frequency fatigue 59 2.2.7.3. Relaxation rate 60 2.2.8. Factors affecting muscle strength 61 2.2.8.1. Ageing 61 2.2.8.1.1. Muscle strength 61 2.2.8.1.2. Muscle mass 63 IV 2.2.8.1.3. Specific force 63 2.2.7.1.4. Contractile properties 64 2.2.8.2. Reproductive hormones 65 2.2.8.2.1. The human menstrual cycle 65 2.2.8.2.2. The menopause 69 3.0. DEVELOPMENT OF EXPERIMENTAL METHODS 72 3.1. Introduction. 72 3.1.1.
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