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Acute changes in endocrine and fluid balance markers during high intensity, steady-state and prolonged endurance running: unexpected increases in oxytocin and brain natriuretic peptide during exercise

T Hew-Butler, Systemic Inflammation Lab, Trauma Research, St Josephs Hospital and Medical Center, Phoenix, 85013, United States
T Noakes, Human Biology, University of Cape Town, Cape Town, South Africa
S Soldin, Core Analytical Lab, Georgetown University Medical Center, Washington DC, United States
J Verbalis, Endocrinology and Metabolism, Georgetown University Medical Center, Washington DC, United States

Correspondence: Tamara Hew-Butler, Email: tamara.hew{at}overhydration.org

Abstract

Maintenance of fluid homeostasis during periods of heightened physical stress can be best evaluated in humans using exercise as a model. Although it is well established that arginine vasopressin (AVP), aldosterone and atrial natriuretic peptide (ANP) are the principle hormones regulating fluid balance at rest, the potential contributions of other related endocrine factors, such as oxytocin (OT) and brain natriuretic peptide (BNP), have not been well described during exercise. Seven endurance-trained runners completed three separate running trials: a maximal test to exhaustion (high intensity), a 60-minute treadmill run (steady-state), and a 56-km ultramarathon (prolonged endurance exercise). Significant pre to post-run increases were found following the ultramarathon in [AVP]p, [OT]p, [NT-proBNP]p, [interleukin-6]p, [cortisol]p, [corticosterone]p and [11-deoxycortisol]p while a significant post-run increase in [aldosterone]p was documented after high intensity, steady state and prolonged endurance running. Similarly, changes in fluid balance parameters were significantly different between the ultramarathon versus high intensity and steady-state running with regard to: plasma volume contraction (less % contraction), body weight loss (increased % weight loss), plasma [Na+] change (decreased from baseline) and urine osmolality change (increase from baseline). Hypothetically-driven relationships between [OT]p versus [AVP]p and between [NT-proBNP]p change versus plasma [Na+] change - combined with the significant and unexpected increases after prolonged endurance exercise - allows for possible speculation that OT and BNP may assist their better known companion hormones (AVP and ANP) in the regulation of fluid balance during conditions of extreme physical stress.