Effects of morning vs evening running on the adipose tissue content during the adolescence of Sprague-Dawley rats

Abstract

The excessive accumulation of adipose tissue leads to overweight and obesity and has a major impact on the lives of millions of adults worldwide. Such accumulation is generally caused by lifestyle habits that break the homeostatic boundaries of major hormones, such as insulin or glucocorticoids. These disorders can be prevented by introducing healthy habits, including adequate diet, sleeping, and regular practice of exercise. However, the experimental manipulation found in human studies is limited compared to that of rodents, making it difficult to address the mechanisms by which these habits reduce the accumulation of adipose tissue in humans, leading to some controversy of results in the literature. In addition, the effects of exercise on the gain of adipose tissue content during adolescence, a vulnerable period for the onset of obesity, are not fully understood. In this thesis, a program of physical activity was developed in adolescent Sprague-Dawley rats to better understand the role of exercise in the gain of adipose tissue during this period of life. For this purpose, a longitudinal body composition assessment was validated using tridimensional computerized tomography. Protocols of controlled exercise were developed to homogenize the locomotor load among all the animals by using motorized running wheels. These protocols were applied in male and female rats, at the beginning and the end of the active period, and under a standard diet. Several transcriptomic, serologic, and circadian parameters were explored to assess the differences between exercising at the beginning or the end of the active phase. The major outcomes of these studies revealed that: a) Adolescence is a period of a greater gain of adipose tissue, compared to the young adulthood of male and female Sprague-Dawley rats. From P30 to P60, both male and female rats gained more adipose tissue than from P60 to P90. b) Male and female rats show differential subcutaneous and visceral adipose tissue content gains during adolescence but not during young adulthood. While males gained more subcutaneous, females gained more visceral adipose tissue during adolescence. c) The effects of exercise on body composition are dependent on the sex during adolescence. Exercise diminished the gain of adipose tissue in males but not in females. d) The effects of exercise on the gain of adipose tissue content depend on the time of the day. Exercise during the late active phase (ZT23) but the not early active phase (ZT13) diminished the gain of adipose tissue during adolescence of male rats only. e) The diminished gain of adipose tissue in rats that exercised during the late active-phase (ZT23) is linked with a delayed sleep phase (as suggested by the core body temperature) and with enhanced lipogenesis and adipocyte glucose uptake (as suggested by the transcriptomic and serologic data). These data contribute to the studies of adolescence, an increasingly recognized period of vulnerability for the onset of metabolic disorders and mental diseases that may carry over to adulthood, translating into health impairment and an economic burden. By using an integrative approach to explore the effects of exercise interventions, adapted to the profile of the individual and that have a major impact on the gain of adipose tissue content during adolescence, the mechanisms participating in those processes may be uncovered, opening new ways to understand this period of life and potentially preventing the onset of diseases that cost millions of lives every year.