Exercise and Endogenous Opiates
Endogenous opiates, endorphins and enkephalins, influence numerous processes within the body including pain, cardiac function, cellular growth, immunity, and blood glucose regulation. Both opiates are released in the brain and stay within the brain compar
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Exercise and Endogenous Opiates Allan H. Goldfarb, PHD CONTENTS Introduction (Endogenous Opiates) Influence of Acute Exercise on bE Levels Aerobic Exercise at Various Work Intensities Related to % VO2 Max (Aerobic Capacity) High-Intensity Bouts with an Anaerobic Component Influence of Training on Beta-Endorphin Levels Influence of Endurance Training Influence of Resistance Training on Circulating bE bE and Immune System Endogenous Opioids and Pain Perception bE and Glucoregulation Influence of Acute Exercise on Enkephalins Summary References
INTRODUCTION (ENDOGENOUS OPIATES) Endogenous opiate-like substances were first discovered in the mid-1970s, when opioid receptors were identified and located within the brain and hypothalamus (80). This led to the discovery that endogenous opioid-like molecules, enkephalins (41) and endorphins (6, 62), were produced within the CNS. Subsequently another class of opiate-like molecules known as dynorphins was identified as being synthesized within the body (33). Endogenous opiates therefore fall into three major classes of substances: endorphins, a peptide of 31 amino acids long; enkephalins, smaller peptide molecules of five amino acids in length (denoted either as leu- or met-, based on the terminal carboxyl amino acid of the peptide); and dynorphins, located in the posterior lobe of the pituitary gland (54) and gastrointestinal tract (35) with a 13 amino acid length.
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_2 © Springer Science+Business Media New York 2013 21
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Goldfarb
Enkephalins were first noted in areas of the brain and parts of the endocrine system. The original studies noted that both endorphins and enkephalins were important regulators of pain (3, 62). However, more recent studies have identified that enkephalins play an important role not only with pain regulation but with certain behaviors, cardiac function, cellular growth, immunity, and ischemic tolerance. Various tissues (heart, smooth and skeletal muscle, kidney, and intestines) in animals and humans have recently been shown to have proenkephalin expression (14). Recently, inflammatory cells were shown to produce and release these opiates, and endorphins seem to be involved not only in immune function (51, 52, 72), pain modulation (93), and the exercise pressor response (43, 73, 97) but also in metabolic control (43, 50, 66, 101). Therefore, there are numerous challenges to be clarified concerning the role of these endogenous opiates, on these processes as they relate to exercise. This is especially true dealing with the control of cellular functions not only under normal conditions but when acute and chronic exercise stress is imposed. Beta-endorphins (bE) were first identified within specific regions of the brain and the hypothalamus. The release of bE into the peripheral circulation was first ascribed to the release from the anterior pituitary gland after being activated by several factors within the hypoth
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