The Effects of Altitude on the Hormonal Response to Physical Exercise
The neuroendocrine system is deeply involved in the adaptive processes to altitude hypoxia, which require a fine-tuned modulation in the homeostatic steady state of several endocrine and metabolic functions. Physical exercise per se is well known to induc
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The Effects of Altitude on the Hormonal Response to Physical Exercise Andrea Benso, MD, N. Prencipe, MD, Stellina Di Giacomo, MD, Fabio Lanfranco, MD, and Silvia Grottoli, MD CONTENTS Introduction Growth Hormone/Insulin-Like Growth Factor-I Axis Prolactin Thyroid Function Gonadal Function Sympathoadrenal System Hypothalamus–Pituitary–Adrenal Axis Antidiuretic Hormone Renin–Angiotensin–Aldosterone System Hormonal Modulation of Energy Balance at High Altitude Conclusions References
INTRODUCTION One of the most important roles of the endocrine system is to allow adaptation to new environmental conditions. The neuroendocrine system “feels” and “informs” the body on such environmental conditions and then triggers biological responses to induce adaptive processes. Most of the studies performed in acute or chronic hypoxic conditions focused on hormones involved in water and electrolyte balance or on the adrenergic system, From: Endocrinology of Physical Activity and Sport: Second Edition Edited by: N. Constantini and A.C. Hackney, DOI 10.1007/978-1-62703-314-5_19 © Springer Science+Business Media New York 2013 363
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whereas scanty data on the other endocrine axes are available. Hormones act through membrane or intracellular receptors (nuclear or cytoplasmic). Hypoxia has been reported to modulate the expression of membrane and nuclear receptors in terms of both down- and upregulation. The study of altitude effects on endocrine variations induced by physical exercise is an extremely interesting but complicated field. Most studies show limitations due to the low reproducibility of experimental protocols, to the number of subjects enrolled, and to the fact that the identification of changes of a single hormone is impaired by the concomitant adaptation of the whole endocrine system in hypoxic conditions. Moreover, several environmental factors affect the endocrine and metabolic response at the same time. For example, high altitude means both hypoxia and low temperature and is a sufficient trigger for appetite suppression and reduced caloric consumption leading to weight loss. Based on the foregoing, in this chapter we summarize literature data and our personal experience.
GROWTH HORMONE/INSULIN-LIKE GROWTH FACTOR-I AXIS Physical exercise is an important environmental regulator of the growth hormone (GH)/insulin-like growth factor (IGF)-I axis activity (1, 2). The GH response to exercise is dependent on the duration and intensity of the exercise bout, the fitness level of the exercising subject, the refractoriness of pituitary somatotroph cells to the exercise stimuli and other environmental factors (3, 4). The neuroendocrine pathways that regulate GH secretion during exercise include the cholinergic, serotoninergic, α-adrenergic, dopaminergic and opioidoergic systems (5–7). The exercise-induced GH release is influenced by fluid intake, environmental and nutritional factors as well as some pathological states (8–11). Gender regulates the relationship between exercise intensity and GH release, since GH secr
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