Mécanismes Adaptatifs et Evolution, UMR CNRS/MNHN 7179, 1 avenue du Petit Château, Brunoy, France.
Exp Gerontol. 2011 Sep;46(9):747-54. doi: 10.1016/j.exger.2011.05.007. Epub 2011 May 19.
Epidemiological evidence related to increased death from hyperthermia suggests higher frailty in the elderly when exposed to high ambient temperatures. Despite the recent awareness of such public health problems, integrative studies investigating the effects of age on the physiological responses to heat wave thermal conditions remain scarce. Daily rhythmicity of core temperature (T(c)) and locomotor activity (LA), as well as parameters representative of energy balance and IGF-1 levels which are involved in the aging process and stress resistance, were monitored in a non-human primate species, the gray mouse lemur (Microcebus murinus). Adult and aged animals, acclimated to long days (LD) or short days (SD), were monitored during 8-day periods of exposure to 25 ° C and 34 ° C. Adult animals displayed efficient coping with heat exposure, regardless of the photoperiod. Hence, efficient responses resulted in decrease of energy intake, energy expenditure, IGF-1 levels and LA levels, promoting hyperthermia avoidance. Positive energy balance was maintained and water turnover did not change significantly after heat exposure. In contrast, while aged animals acclimated to LD responded similarly to adults, aged mouse lemurs acclimated to SD showed great difficulties coping with heat exposure. Indeed, in this group, normothermia impairment was associated with increased T(c) levels, alterations in daily rhythmicity, negative energy balance and increased IGF-1 levels. Impaired responses to heat exposure were seen in aged mouse lemurs acclimated to SD only. The main effects were observed during diurnal resting periods, suggesting decreased capacities with age to dissipate excess body heat. Taken together, these data highlight daily rhythmicity and IGF-1 pathway as main targets in the impaired response to heat exposure in the elderly.
与高温导致过热死亡相关的流行病学证据表明，老年人在暴露于高温环境时身体更为脆弱。尽管最近已经意识到存在这样的公共卫生问题，但仍缺乏综合研究来调查年龄对热浪热条件下生理反应的影响。在一种非人类灵长类动物——灰鼠狐猴（Microcebus murinus）中，监测了核心体温（T(c)）和运动活动（LA）的日常节律以及与衰老过程和应激抵抗相关的能量平衡和 IGF-1 水平的代表性参数。成年和老年动物适应长日照（LD）或短日照（SD），在暴露于 25°C 和 34°C 的 8 天期间进行监测。成年动物无论光照周期如何，都能有效地应对热暴露。因此，有效的反应导致能量摄入、能量消耗、IGF-1 水平和 LA 水平降低，从而避免体温过高。在热暴露后，正能量平衡得以维持，水周转率没有明显变化。相比之下，适应 LD 的老年动物与成年动物的反应相似，而适应 SD 的老年鼠狐猴在应对热暴露方面则存在很大困难。实际上，在这个群体中，体温调节障碍与 T(c)水平升高、日常节律改变、负能量平衡和 IGF-1 水平升高有关。仅在适应 SD 的老年鼠狐猴中观察到对热暴露反应受损。主要影响发生在日间休息期间，这表明随着年龄的增长，身体散热能力下降。综上所述，这些数据突出了日常节律和 IGF-1 途径作为老年热暴露反应受损的主要靶点。
