Obesity occurs when nutrient intake exceeds energy expenditure over prolonged periods. In the modern world, obesity has reached epidemic proportions. Complications of obesity, including cardiovascular disease, non-alcoholic fatty liver disease, certain forms of cancer, and metabolic dysfunction contribute substantially to morbidity and death today. With 13% of the world’s population affected, the rising rates of obesity will grow as a public health burden. Until recently, pharmacologic attempts to treat obesity have focused on reducing food intake. However, motivated in part by recent studies in mice and by analyses of fat in humans, approaches to increasing energy expenditure, specifically thermogenic energy expenditure, may provide a new therapeutic avenue. Most simplistically, there are two classes of adipocytes: storage and thermogenic. Storage fat, typically composed of unilocular white adipocytes function as storage depots for excess calories. On the other hand, thermogenic fat containing brown or beige adipocytes, generate heat through uncoupled mitochondrial respiration, This regulated generation of heat, known as thermogenesis, is used by organisms to maintain or increase body temperature. Historically, thermogenesis has been divided into shivering and nonshivering thermogenesis. Repeated, rapid contraction of skeletal muscles generate heat and is the basis for shivering thermogenesis. Nonshivering thermogenesis (NST) describes all the other mechanisms by which an organism can generate regulated heat. Only two organelles are known to contribute to NST: the mitochondrion of brown and beige adipocytes and the sarcoplasmic reticulum of muscle. The role of other organelles has not been systematically studied. Here we show in mice that thermogenic stimuli, including a cold challenge and pyrogenic molecules, activate a lysosomal program in a known thermogenic tissue (BAT) as well as several “non-thermogenic” organs, including the spleen, liver and skeletal muscle. A similar program is activated by a cold challenge in the metazoan, Drosophila melanogaster, suggesting an evolutionarily ancient origin for this response. We show by both pharmacologic and genetic means that impairment of lysosomal function compromises the thermogenic response of individual cells ex vivo and of mice in vivo. Data from genetic manipulations find that impairment of lysosome function that leads to cold intolerance and death can modestly downregulate the classical Ucp1 thermogenic program. However, pharmacological inhibition reveals that impairment of lysosome function can compromise thermogenesis without altering the Ucp1 program. As part of our efforts to study lysosome function in thermogenesis we developed a new method of measuring thermogenesis in primary cells. Using isothermal titration calorimetry (ITC), we quantitatively measured the heat generated by cells isolated from mice. This permitted us to assess the effects of both genetic and pharmacologic manipulations on the generation of heat and allowed us, for the first time, to measure the heat (uCal/sec/cell) of BAT in the basal and stimulated state. With ITC, we demonstrated that the impairment of lysosome function had direct effects on the generation of cellular heat, independent of systemic modulators of temperature such as basal metabolic rate or circulatory dissipation. From these studies, we conclude that lysosomes are thermogenic organelles induced by cold and pyrogenic stimuli and contribute both directly and indirectly to thermogenesis. Our work also suggests that lysosome thermogenesis may provide a means of thermoregulation in non-homeotherms as well as in tissues previously not implicated in temperature regulation in mammals.

Thesis (Ph.D.)--Indiana University, 2010. / Title from screen (viewed on March 3, 2010). Department of Pharmacology and Toxicology, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Joseph A. DiMicco, Sherry F. Queener, Daniel E. Rusyniak, Michael R. Vasko. Includes vitae. Includes bibliographical references (leaves 126-147).

In man the metabolic heat produced during physical exercise stresses the thermoregulatory system, particularly if hot, humid environmental conditions prevail. It has recently been postulated that endogenous opioids may play a role in regulating body temperature at rest and because it has also been shown that blood levels of these substances increase during exercise, the possibility exists that endogenous opioids may play a role in thermoregulation during exercise. A study was conducted in two parts to determine the thermoregulatory response during exercise with and without pharmacologic blockade of the opioid receptor. In Part I nine healthy male subjects performed 30 minutes cycling at 50 % maximal aerobic capacity in an environmentally controlled laboratory. The subjects received either placebo, 2mg or 10mg naloxone hydrochloride in a randomized double-blind crossover fashion prior to the exercise test. Rectal temperatures were recorded at one-minute intervals and cardiorespiratory parameters were measured during the test. Water loss was calculated from differences in nude body weight. In part II eight male subjects performed a graded maximal cycle ergometer test after receiving either placebo or 2mg naloxone in a randomized double-blind crossover fashion. Rectal and sublingual temperatures were recorded before and after the test and oesophageal temperature was recorded at one-minute intervals during the test. Cardiorespiratory parameters were recorded during the test. The results of Part I show that rises in rectal temperature as well as calculated water losses were similar for placebo and after the administration of both 2mg and 10mg naloxone. Similarly, during maximal exercise (Part II) the rise in rectal and oesophageal temperatures was equivalent for placebo and 2mg naloxone but sublingual temperature failed to rise during exercise following the 2mg naloxone dose. Cardiorespiratory responses did not differ between placebo and naloxone tests in both Part I and Part II of the study. These results indicate that naloxone-mediated blockade of opioid receptors does not affect rectal and oesophageal temperature responses to either submaximal or maximal exercise. Naloxone appears to selectively alter the sublingual temperature response to exercise possibly by altering local blood flow. It is concluded that insofar as naloxone induced opioid receptor blockade provides a measure of the function of the endogenous opioid system, this study suggests that the endogenous opioid system does not play a significant role in thermoregulation during exercise.

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Call number: LD2668 .T4 1978 H35 / Master of Science

Call number: LD2668 .T4 1979 W33 / Master of Science

Thermoregulatory, analgesic and respiratory depressive responses as well as tolerance to morphine were investigated in young (3 to 5 months), mature (10 to 12 month) and senescent (26 to 28 month) male Fischer 344 rats. The thermoregulatory system of senescent rats was not able to maintain body temperature in hot and cold environments as well as the thermoregulatory system of young rats. Additionally, senescent rats had basal rectal temperatures which were approximately one degree lower than basal temperatures in young rats. Subcutaneous morphine caused biphasic effects on body temperature ie. hyperthermia at low doses and hypothermia at high doses. Senescent rats were less responsive to the hypothermic effects of subcutaneous morphine than young rats, but this was not due to decreased subcutaneous blood flow or inability to lose heat. Morphine injections intracerebroventricularly showed no age-related differences. A two site model for the actions of morphine on thermoregulation was proposed and it was suggested that the age-related differences are due to changes in a non periventricular site. Previously reported increased lethality of intravenous morphine in aged rodents was shown to be due to decreased respiratory reserve rather than increased sensitivity to respiratory depression. Senescent rats were also found to acquire tolerance to the thermic effects of morphine less readily than young rats regardless of the route of administration. Normal aging has been characterized as a decrease in adaptability, and it was suggested that senescent rats were less able to compensate for the thermic effects of morphine as well as young rats. In order to determine the mechanisms of decreased adaptability, neurotransmitters proposed to be involved in thermoregulation were injected intracerebroventricularly in morphine tolerant rats. The results suggested a shift from catecholaminergic to cholinergic transmitters with aging.

Endothermic homeothermy is a major feature of the adaptive suites of tachymetabolic animals such as mammals and birds. The advantages homeothermy confers on birds and mammals include relative independence from the environment, a stable internal milieu, and possibly the ability to sustain high aerobic activity (Bennett and Ruben 1979). Some mammals in situations of limited water or energy availability, however, depart markedly from homeothermy and instead display patterns of heterothermy. Torpor is a lowering of body temperature (T(b)) to conserve energy and/or water. I studied the energetics of arousal from torpor in two desert pocket mice species. The species differed in warming rates and arousal durations, but used similar amounts of energy to arouse. The smaller species, Perognathus amplus, lost mass more quickly while fasting in the cold, yet waited as long as the larger species, Chaetodipus baileyi, before entering torpor. P. amplus maintained a lower T(b) during topor than C. baileyi. The thermodynamics of arousal indicated that metabolic rate during arousal was a function of T(b) but not ambient temperature (Tₐ), that the animals changed thermal conductance to increase heat gain when Tₐ was greater than T(b), and that Q₁₀ decreased during arousals. In contrast to torpor, adaptive hyperthermia provides desert mammals in dry, hot environments a means to conserve water that would normally be used for evaporative cooling. I modeled the effects of body size on adaptive hyperthermia and discovered that small mammals gain the most in terms of water savings using this strategy, and that small and large mammals can spend larger fractions of the day active than do medium size mammals. I demonstrated that two desert ground squirrel species make use of adaptive hyperthermia during the summer near Tucson, Arizona by following free-ranging squirrels implanted with temperature-sensitive radio transmitters. Ground squirrel T(b) fluctuated almost continuously, ranging from about 35°C to over 42°C, and rarely approached steady state. Of the two species studied, Ammospermophilus harrisii had higher mean T(b), similar maximum T(b), and lower T(b) variability compared to Spermophilus tereticaudus. These results are consistent with the more wide-ranging foraging style of A. harrisii compared to S. tereticaudus.

Muitos animais enfrentam situações de baixa pressão parcial de oxigênio (hipóxia) ao longo da vida, seja por condições ambientais (tocas, altas altitudes) ou clínicas (insuficiência cardíaca, respiratória ou metabólica). Sabe-se que a queda regulada da temperatura corporal (Tc), chamada anapirexia, induzida pela hipóxia tem tanto importância fisiológica quanto para a clínica, entretanto apenas nas últimas décadas alguns pesquisadores têm se dedicado mais intensamente ao estudo dos mecanismos envolvidos neste fenômeno. Estes estudos, em geral, não levaram em conta a fase do dia durante a realização dos experimentos nem durante a análise dos resultados. Considerando que a Tc apresenta um ritmo diário e circadiano com padrão robusto, é possível que a anapirexia seja alterada de acordo com o momento do dia em que o animal é exposto à hipóxia. Diante disso, tal hipótese foi testada no presente estudo e, para isso, os animais foram expostos à hipóxia em diferentes fases do dia e foi registrada a Tc, o consumo de oxigênio (VO2) e o índice de perda de calor (IPC). Estes protocolos foram realizados sob duas temperaturas ambientes (Tas; 26 e 19°C), pois se sabe que a anapirexia também pode ser alterada pela Ta. Em ambas Tas, foi visto que animais expostos à hipóxia no início da fase de escuro apresentam amplitude maior de queda de Tc em relação àqueles expostos no início da fase de claro e, tal diferença deve-se, ao menos em parte, à inibição induzida pela hipóxia da maior termogênese encontrada nestes animais durante a noite. O IPC mensurado no final do intervalo hipóxico parece não ter muita importância para as diferenças nas respostas anapiréticas. Além disso, todas as amplitudes anapiréticas foram maiores nos animais testados sob o frio, independente da fase do dia. Assim, os resultados indicam que a fase do dia interfere na anapirexia induzida por hipóxia aguda e que essa resposta é maior em menores Tas em qualquer momento do dia. / Several animals face reduced oxygen partial pressure (hypoxia) throughout their lives, due to environmental (burrows, high altitudes) or clinical conditions (cardiac, respiratory or metabolic failures). Its known that the hypoxia-induced decrease in body temperature (Tb), named anapyrexia, is a regulated process of adaptive importance. However only in the past few decades researchers have been studied the mechanisms involved in this phenomenon. These studies, in general, did not take the phase of the day into account during the experiments or during the analyses of their results. Considering that Tb shows circadian and diary rhythm with a robust pattern, it is possible that anapyrexia can be altered depending on to the moment of the day in which the animal is exposed to hypoxia. Thus, the present study tested this hypothesis exposing animals to hypoxia in different phases of Day and Tb, oxygen consumption (VO2) and heat loss index (HLI) were measured. These protocols were conducted in two ambient temperatures (Tas; 26°C and 19°C), because it is known that anapyrexia can be altered by Ta. In both Tas, it was observed that animals exposed to hypoxia during the beginning of the dark phase presented bigger anapyrexic amplitude than those exposed during the beginning of the light phase. This difference may be due, at least in part, to the inhibition induced by hypoxia of the biggest thermogenesis found during dark phase. HLI measured at the end of the hypoxia exposure seems to have no influence in the different anapyretic responses. Moreover, the cold condition induced bigger anapyretic responses independent on the phase of day. Thus, the results indicate the phase of day influences the hypoxia-induced anapyrexia and this response is bigger in lower ambient temperatures at any moment of the light-dark cycle.

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