The concept of this book has developed over the past fi fteen years as interest in the water and electrolyte disturbances associated with most environmental settings moved from a research area of descriptive discovery to one dealing with the mechanisms responsible for the previously observed disturbances. Most of the contributing authors have been involved in both aspects of this evolution of research, focusing on those problems associated with body fluid and electrolyte balance and searching for hormonal explanations. What did not accompany this transition, however, was a source of information encompassing the area of interest. Instead, the previous format of environmentally focused symposia, reviews, and books continued to be the only sources available. For instance, various books deal with the physiology of high altitude, space, or exercise but do not necessarily provide adequate coverage of water and electrolyte disturbances. To our knowledge, the format of this book is unique. We have made the central focus water and electrolyte physiology with an emphasis on endocrinology and tried to comprehensively cover this area of physiology in some of the more heavily studied environments. This book too, then, will have its limitations in coverage. For instance, in-depth coverage of the respiratory and cardiovascular responses to the high altitude en vironment will not be found, but since these areas are so integrally associated with water and electrolyte regulation they are not ignored.

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1 Fluid and Electrolyte Homeostasis During and Following Exercise: Hormonal and Non-Hormonal Factors.- Non-Hormonal Effects of Exercise.- Water and Electrolyte Balance during Exercise.- Thirst and Fluid Intake.- Renal Responses to Exercise.- Summary of Fluid and Electrolyte Homeostasis During Exercise.- Hormonal Effects of Exercise.- Vasopressin.- Atrial Natriuretic Peptide.- Renin-Angiotensin System.- Aldosterone.- Other Hormones.- Factors Modulating Hormonal Responses to Exercise.- Summary.- Conclusion.- References.- 2 Hormonal Regulation of Fluid and Electrolytes: Effects of Heat Exposure and Exercise in the Heat.- Effects of Exogenous Hormones.- Sedentary Heat Exposure.- Exercise in the Heat.- Hypohydration.- Electrolytes.- Heat Acclimation.- Plasma Volume.- Future Studies.- Conclusion.- References.- 3 Effect of Exposure to Cold on Fluid and Electrolyte Exchange.- Effects of Exposure to Cold on Water Intake.- Effects of Acute Exposure to Cold in Rats.- Duration of Exposure to Cold Required to Induce Thermogenic Drinking in Rats.- Effects of Food Intake on Water Intake in the Cold.- Effects of Cold on Urine Production: Role of Antidiuretic Hormone.- Mechanism of Thermogenic Drinking.- Role of the Renin-Angiotensin System in Thermogenic Drinking.- Effect of a Ten-Day Cold Exposure on Electrolyte Exchange.- Effect of Dietary Bulk on Water and Electrolyte Exchange in the Cold.- Fluid Exchange During Four Weeks of Exposure to Cold.- Water Balance in Man Exposed to Cold.- Comments.- References.- 4 Hormonal and Renal Responses to Hyperbaria.- Urinary Responses to Hyperbaric Exposure.- Body Fluid Balance During Hyperbaric Exposure.- Endocrine Responses.- Antidiuretic Hormone (ADH).- Renin-Aldosterone.- Prolactin.- Prostaglandin E2 (PGE2).- Parathyroid Hormone (PTH).- Atrial Natriuretic Factor (ANF).- Characteristics of Hyperbaric Nocturia.- Hydrostatic Pressure Effect on Active Na Transport.- Summary.- References.- 5 Head-Out Water Immersion: A Critical Evaluation of the Gauer-Henry Hypothesis.- Water Immersion as a Model of Hypervolemia.- Species Effects on Water Immersion Responses.- Methodological Considerations of the WI Model.- Cardiovascular Receptors.- Cardiac Receptors.- Arterial Baroreceptors.- Cardiovascular Effects of WI.- Hypervolemia in WI.- Regional Blood Flow in WI.- Renal Responses to WI.- Hormonal Responses to WI.- Vasopressin.- Renin and Aldosterone Secretion.- Atrial Peptides.- Renal Prostaglandins.- Circulating Catecholamines.- Role of the Renal Sympathetic Nerves.- Influence of Circadian Rhythms.- Effects of Water Temperature.- Conclusions.- Acknowledgements.- References.- 6 Fluid and Electrolyte Balance and Hormonal Response to the Hypoxic Environment.- Effects of Hypoxia on Water and Electrolyte Balance.- Evidence for Hypohydration at High Altitude.- Effects of High Altitude on Electrolytes.- Mechanisms of Hypoxia-Induced Hypohydration.- Effects of Hypoxia on Thirst and Mechanisms of Control.- Effects of Hypoxia on Urine Flow.- Inhibition of ADH in Response to Acute Mild Hypoxia.- Stimulation of ADH Release by Hypoxia.- Effects of Hypoxia on Glucocorticoids.- Mechanisms of Salt Imbalances.- Atrial Natriuretic Factor Responses to Hypoxia.- Inhibition of Aldosterone by Hypoxia.- Hormones and Altitude Sicknesses.- Summary.- References.- 7 Hormonal Regulation of Fluid and Electrolytes During Prolonged Bed Rest: Implications for Microgravity.- Bed Rest.- First day.- First month and beyond.- Fluid Shifts in Microgravity.- Summary and Conclusions.- References.