Rest-Phase Hypothermia Reveals a Link Between Aging and Oxidative Stress: A Novel Hypothesis

Abstract

In endotherms, growth, reproduction, and survival are highly depended on energy metabolism. Maintenance of constant body temperature can be challenging for endotherms under continuously changing environmental conditions, such as low or high ambient temperatures or limited food. Thus, many birds may drop body temperature below normothermic values during the night, known as rest-phase hypothermia, presumably to decrease energy metabolism. Under the assumption of the positive link between aerobic metabolism and reactive oxygen species, it is reasonable to suggest that low body temperature, a proxy of energy metabolism, will affect oxidative stress of the birds. Aging may considerably affect behavior, performance and physiology in birds and still requires further investigation to understand age-specific changes along the lifespan of the organism. Until today, age-specific rest-phase hypothermic responses and their effect on oxidant-antioxidant status have never been investigated. We exposed 25 zebra finches (Taeniopygia guttata) of three age classes, 12 young birds (1.1–1.3 years old), 8 middle-aged (2.4–2.8 years old), and 5 old birds (4.2–7.5 years old) to day-long food deprivation or provided them normal access to food under thermoneutral conditions. We compared night-time body temperature, measured through implanted data loggers, and quantified plasma oxidative status (uric acid, antioxidant capacity, and d-ROM assay) the following morning. We found age-related differences in night-time body temperature following a day-long food deprivation while all three age groups remained normothermic in the night following a day with access to food. The lowest minimum body temperature (LSM ± SE: 36.6 ± 0.2°C) was observed in old individuals during rest-phase hypothermia. Surprisingly, these old birds also revealed the highest levels of plasma oxidative damage, while young and middle-aged birds maintained higher night-time body temperature and showed lower values of oxidative damage. These results lead us to propose a novel hypothesis on how aging may lead to an accumulation of oxidative damage; the impaired physiological capacity to thermoregulate with advancing age does increase the risk of oxidative stress under challenging conditions. When energy is limited, the risk to encounter oxidative stress is increasing via a compensation to defend normothermic body temperatures.

An Overview of the Implications for Perianesthesia Nurses in terms of Intraoperative Changes in Temperature and Factors Associated with Unintentional Postoperative Hypothermia

“…Hypothermia is characterised by widespread metabolism reduction that affects all bodily systems at the same time. Between 50 and 90 percent of surgery patients suffer from hypothermia at some point throughout their recovery period [ 4 , 5 ]. The consequence is significant physiological alterations, including changed heart function, fluctuations in state of awareness, shivering and extended plasma half-lives of medicines, which may also enhance oxygen consumption by up to 500 percent [ 6 – 8 ].…”

Plasticity of mitochondrial function safeguards phosphorylating respiration during in vitro simulation of rest-phase hypothermia

“…It is possible, therefore, that rest-phase hypothermia may come at the cost of increased oxidative stress (cf. 57 ). It is interesting to note that this acute response to reduced air temperature is opposite to what has been recorded as part of seasonal acclimatisation in the same model system 20 and in response to cold exposure in tissues with more clearly defined metabolic or thermogenic roles in other models (see references above).…”

“…it is possible that rest-phase hypothermia may come at the cost of increased oxidative stress [cf. 57]. Future work should explore this hypothesis by direct measurement of ATP- and ROS production, and membrane potential, to conclude on the consequences of changes to the efficiency of phosphorylating respiration for redox balance in normo- and hypothermic birds.…”

The effects of bathing in neutral bicarbonate ion water

“…Thermoregulatory function declines with aging 29 , and one of the causes is an aging-associated decrease in production of NO, which has a vasodilator effect 30 . Some researchers reported that poorer thermoregulation with aging is related to suppression of mitochondria metabolism, increased ROS production, and accumulated oxidative damage to cells 31 . Thus, because aging is related to cold intolerance, the results of this study can be generalized only to middle-aged and older people.…”