Hormonal responses to opioid receptor blockade: during rest and exercise in cold and hot environments

Abstract

Opioid receptors appear to modulate a variety of physiological and metabolic homeostatic responses to stressors such as exercise and thermally extreme environments. To more accurately determine the role of the naloxone (NAL) sensitive opioid receptor system during rest and exercise, subjects were subjected to concomitant environmental thermal stress. Fifteen untrained men rested or performed low intensity (60% VO2peak) or high intensity (80% VO2peak) exercise on a cycle ergometer for 60 min in an environmental chamber during cold (0 degrees C) hot (35 degrees C) air exposure while receiving an infusion of normal saline (SAL) or NAL (0.1 mg kg(-1)). Plasma adrenocorticotropin hormone (ACTH), immunoreactive beta-endorphin (IBE), cortisol and growth hormone were measured at baseline and every 15 min while in the chamber. Time to exhaustion was significantly reduced during high intensity exercise in the heat (P<0.0001). NAL significantly (P=0.0004) reduced the time to exhaustion (38.3+/-2.1 min) during high intensity exercise in the heat compared to SAL (49.4+/-2.1 min). ACTH and IBE increased during hot conditions and cold attenuated this response. Plasma concentrations of IBE, ACTH, and growth hormone increased significantly with NAL during high intensity exercise in the heat compared to SAL. Cold attenuated the response of ACTH, IBE and cortisol to NAL. NAL administration exaggerates plasma hormone concentration during high intensity exercise in the heat, but not cold. These results support a regulatory effect of the opioid receptor system on physiological responses during exercise in thermally stressful environments. Future research should be directed to more clearly defining the effect of environmental temperature on the mechanism of hypothalamic-pituitary-adrenal hormonal release during exercise and hot environmental temperatures.

Postmortem biochemistry and immunohistochemistry of adrenocorticotropic hormone with special regard to fatal hypothermia

“…Previous studies showed that exposure to cold air attenuated the increase in ACTH and b-endorphine concentrations in response to high-intensity exercise and drug administration [6]. These findings suggest that ACTH can be used as a marker of fatal hypothermia.…”

Hormonal responses to a 160-km race across frozen Alaska

“…Furthermore, the opioid receptor system seems to regulate the physiological responses to exercise in thermally stressful environments 27. Nevertheless, responses of GH, cortisol and testosterone to these contradicting stresses is unknown and presents a unique summated stress to the athlete.…”

Beta-adrenergic and Opioidergic Modulation of Cortisol Secretion in Response to Acute Stress

“…However, the inhibition of beta-adrenoceptors did not affect the cortisol response to stress of 5-min exercise in pigs ( Weiss et al, 1974 ). Different stressors activate the hypothalamic-pituitary-adrenal axis together with increased endogenous opioid activity ( Akil et al, 1984 ;Der-Avakian et al, 2005 ;Armstrong, 2006 ;Rushen et al, 1993 ). Naloxone increased ACTH and cortisol in resting as well as restrained gilts ( Janssens et al, 1995 ;Rushen et al, 1993 ).…”