Cardiovascular PET-CT
Yi-Hwa Liu, Albert J. Sinusas in Hybrid Imaging in Cardiovascular Medicine, 2017
PET-CT viability imaging is performed with a combination of a perfusion radionuclide such as Rb-82 or 13NH3 to identify resting perfusion defects, compared with FDG, to identify areas of “viable” hibernating myocardium within the areas of decreased perfusion. A CT scan is performed for accurate attenuation correction. Hibernation refers to a phenomenon of altered metabolism within chronically ischemic myocardium with contractile dysfunction, where there is an increase in anaerobic glycolysis. This occurs in response to repeated ischemic insults and is of clinical significance, as normal contractile function may be restored by revascularization of these areas, and the degree of hibernating myocardium has been shown to predict improved outcomes following successful revascularization (D’Egidio et al. 2009) and may be a better predictor than inducible ischemia in these patients (Ling et al. 2013).
Summary and Development of a New Approach to Senescence
Nate F. Cardarelli in The Thymus in Health and Senescence, 2019
Circulating lymphocytes, serum complement immunoglobulin, and thymosin levels, as well as other elements of the immune system display circadian rhythmicity. Some have asserted that the thymus is a biological clock, though evidence is rather scanty. Thymus transplants from normal mice to one strain of dwarf mice will extend lifetime from around 4 months to 6 months. The thymus gland involutes during hibernation, then rejuvenates just before arousal, thus following a circannual rhythm. Interestingly, even though one would suppose that the immune system would lose capability as the thymus involutes, the appearance and growth of malignant tumors, and metastasis are much lower during hibernation.153 The differences between subjects and controls prevented from hibernation appear too great to be merely a matter of reduced metabolic rate. Hibernating species, such as the bat, show a much longer life-span (20 years) as compared with related nonhibernators (e.g., 2 to 3 years for mice and rats). Morphology of the pineal also changes during hibernation, and melatonin levels decrease substantially. It has been suggested that the pineal pacemaker in the hamster is arrested in the day phase of the cycle during hibernation.
Investigating links between diet and health outcomes
Geoffrey P. Webb in Nutrition, 2019
There are thus occasions, such as enforced fasting, when even the most commonly used experimental animals, mice, “abandon” the energy-expensive struggle to maintain “normal” 37°C body temperature for several hours at a time. Some other mammals like hamsters, hedgehogs, bats and dormice spend many winter weeks or months in hibernation where their metabolism and heart rate slows and their body temperature drops close to the environmental temperature. Anyone who has kept a garden pond will know that, unlike mammals, fish eat less in cold weather. The body temperature of fish and other non-mammalian vertebrates fluctuates with environmental temperature. In these so-called poikilotherms, metabolism is slower in the cold whereas non-hibernating, homeothermic mammals increase their metabolic rate in an attempt to maintain their high body temperature. It is obvious that fish would be a poor guide to the effect of environmental temperature on food intake in mammals but it seems that the less well-known ability of mice to become torpid also makes some experiments with mice an unreliable guide to human responses.
Chlorpromazine and promethazine reduces Brain injury through RIP1-RIP3 regulated activation of NLRP3 inflammasome following ischemic stroke
Published in Neurological Research, 2021
Qian Jiang, Mélissa Wills, Xiaokun Geng, Yuchuan Ding
Hibernation is a unique physiologic process that is seen in various mammalian species [14] in which metabolic rates are lowered to decrease body temperatures by up to 2.9°C [17]. Many studies suggest that this state of reduced metabolic ability plays an important role in neuroprotection as it confers a greater tolerance to hypoxic and hypoglycemic states, and thereby is proposed to be of neuroprotective value during cerebral ischemia [10]. Furthermore, the post-stroke inflammatory response, which is involved in ischemic stroke pathogenesis, has also been shown to be attenuated in hibernating animals [18]. Indeed, the typical inflammatory response of euthermic brain tissue, such as microglia activation and leukocytopenia, both were suppressed in hibernating animals when compared to their non-hibernating counterparts [19].
Hypothalamus but not liver retains daily expression of clock genes during hibernation in terai tree frog (Polypedates teraiensis)
Published in Chronobiology International, 2020
Bijoy Krishna Borah, Zothanmawii Renthlei, Amit Kumar Trivedi
Vertebrate organisms adjust the period of endogenous clock(s) to correspond to annual photoperiod changes to perform seasonal physiological processes like hibernation, migration, and reproduction (Helm et al. 2013; Kumar et al. 2010). These seasonal breeders differ in their physiology during different seasons of the year and is called annual life history states (Trivedi et al. 2014). To respond to the environmental photoperiod cycle, organisms require behavioral and physiological plasticity (Stevenson and Ball 2011). To cope with adverse environmental conditions, organisms have evolved different strategies. Invertebrate organisms (insects) undergo dormancy called diapause (Bradshaw and Lounibos 1977), while some higher animals either migrate (Kumar et al. 2010) or hibernate/aestivate (Williams et al. 2017) during unfavorable environmental conditions. Hibernation is an energy conservation strategy to cope with adverse environmental conditions (Carey et al. 2003; Roots 2006). During hibernation, metabolic rate, heart rate, and oxygen consumption can all be reduced (Storey and Storey 2004). Hibernation physiology has been extensively investigated in mammals (Fedorov et al. 2009; Geiser 2004; Lei et al. 2014; Ruf and Geiser 2015; Storey and Storey 2004; Yan et al. 2006), with emphasis mostly on metabolic genes, which are differentially expressed during hibernation (Srere et al. 1992; Williams et al. 2005).
Influences of ovarian hormones on physiological responses to cold in women
Published in Temperature, 2022
Andrew M. Greenfield, Nisha Charkoudian, Billie K. Alba
The existence and functional nature of BAT has long captivated the scientific community since its discovery in the 16th century [55]. Remarkably, this brown, multilocular tissue has inspired multiple resurgences in concerted research efforts for over four centuries. Early observations in hibernating rodents found BAT to be highly thermogenic, defending against decreases in core temperature and serving as a mechanism for energy homeostasis [56]. Given the significantly larger body surface area (BSA)-to-mass ratio of rodents relative to humans, it could be speculated a greater reliance on BAT thermogenesis would be expected and beneficial to survival. While abundant in small mammals, BAT in humans was thought to exist only in newborns, with atrophy occurring throughout infancy and minimal levels soon after [57]. This diminution of BAT raised speculation that its purpose was physiologically inconsequential in adult humans. Nonetheless, the potential for anti-obesity therapeutics (e.g., potential for burning extra calories without exercise) remained a significant and perpetuating impetus for the continuation of BAT research in rodents [58].