- Switching on the furnace: regulation of heat production in brown adipose tissue. [Journal Article]
- MAMol Aspects Med 2019 Jul 17
- Endothermy requires a source of endogenous heat production. In birds, this is derived primarily from shivering, but in mammals it is mostly non-shivering thermogenesis (NST). Brown adipose tissue (BA…
Endothermy requires a source of endogenous heat production. In birds, this is derived primarily from shivering, but in mammals it is mostly non-shivering thermogenesis (NST). Brown adipose tissue (BAT) is a specialized tissue found in Eutherian mammals that is the source of most NST. Heat production in BAT depends primarily on the activity of uncoupling protein 1 (UCP1), which decouples transport of protons across the inner mitochondrial membrane from synthesis of ATP. UCP1 and hence heat production of BAT is regulated by many factors. In this paper we discuss the main factors activating UCP1 and increasing heat production. Probably the most well-known activator is the catecholamine norepinephrine (NE) which is released from sympathetic nerve endings and binds to adrenergic receptors that are abundantly expressed on BAT. NE stimulates release of free-fatty acids. It was previously thought that such FFAs were essential for activation of UCP1. However recent work has suggested intracellular lipolysis is not essential and FFAs can be derived from extracellular sources. Thyroid hormones also exert impacts on metabolic rate via effects on brown adipocytes which express type 2 deiodinase. Knocking out DIO2 makes mice cold intolerant. Parathyroid hormone appears to also be a potent regulator of BAT activity and may be an important mediator of elevated expenditure during cancer cachexia, although this is disputed by observations that cachexia wasting is not blunted in UCP1 KO mice. Cardiac natriuretic peptides have also been implicated in regulating BAT thermogenesis and the interconversion of beige adipocytes from their white to brown form. Activation of BAT thermogenesis may be an important component of the post-ingestion rise in heat production. Recent work suggests the gut derived hormone secretin may play a key role in this effect, directly linking BAT activation to the alimentary tract. Not only gut hormones but also metabolites derived from gut microbiota such as butyrate may be an important activator of BAT during cold exposure. Additional regulatory factors include bone morphogenic proteins, fibroblast growth factor 21, Vascular endothelial growth factors and transient receptor potential vanilloid receptors which are important components of thermal sensing and hence how brown adipose tissue responds to the cold. In the future the main challenge is to understand how these regulatory factors combine with each other and with inhibitory factors to control heat production from BAT, and what their relative importance is in differing circumstances. Knocking out UCP1 has revealed other sources of heat production in BAT including creatine-dependent cycles and a futile cycle of Ca2+ shuttling into and out of the endoplasmic reticulum via the SERCA and ryanodine receptors.
- Ontogenetic change in the amount and position of slow-oxidative myotomal muscle in relationship to regional endothermy in juvenile yellowfin tuna Thunnus albacares. [Journal Article]
- JFJ Fish Biol 2019 Jul 11
- Myotomal slow-oxidative muscle (SM) powers continuous swimming and generates heat needed to maintain elevated locomotor muscle temperatures (regional endothermy) in tunas. This study describes how th…
Myotomal slow-oxidative muscle (SM) powers continuous swimming and generates heat needed to maintain elevated locomotor muscle temperatures (regional endothermy) in tunas. This study describes how the amount and distribution of myotomal SM increases with fish size and age in juvenile yellowfin tuna Thunnus albacares in relationship to the development of regional endothermy. In T. albacares juveniles 40-74 mm fork length (LF ; n = 23) raised from fertilised eggs at the Inter-American Tropical Tuna Commission Achotines Laboratory in Panama and larger juveniles (118-344 mm LF ; n = 5) collected by hook and line off of Oahu, Hawaii, USA, SM was identified by histochemical staining for the mitochondrial enzyme succinic dehydrogenase or by colour (in the two largest individuals). The cross-sectional area of myotomal SM at 60% LF , a position with maximal per cent SM in larger T. albacares, increased exponentially with LF . The percentage of total cross-sectional area composed of SM at 60% LF increased significantly with both LF and age, suggesting that SM growth occurs throughout the size range of T. albacares juveniles studied. In addition, the percentage of SM at 60% LF that is medial increased asymptotically with LF . The increases in amount of SM and medial SM, along with the development of the counter-current heat-exchanger blood vessels that retain heat, allow larger tuna juveniles to maintain elevated and relatively stable SM temperatures, facilitating range expansion into cooler waters. This article is protected by copyright. All rights reserved.
- Cardiovascular and ventilatory interactions in the facultative air-breathing teleost Pangasianodon hypophthalmus. [Journal Article]
- JCJ Comp Physiol B 2019 Jul 04
- All vertebrates possess baroreceptors monitoring arterial blood pressure and eliciting reflexive changes in vascular resistance and heart rate in response to blood pressure perturbations imposed by, …
All vertebrates possess baroreceptors monitoring arterial blood pressure and eliciting reflexive changes in vascular resistance and heart rate in response to blood pressure perturbations imposed by, e.g., exercise, hypoxia, or hemorrhage. There is considerable variation in the magnitude of the baroreflex amongst vertebrate groups, making phylogenetic trends and association with major evolutionary events such as air-breathing and endothermy, difficult to identify. In the present study, we quantified the baroreflex in the facultative air-breathing catfish Pangasianodon hypophthalmus. Using a pharmacological approach, we quantified the cardiac limb of the baroreflex and by subjecting fish to hypoxia and by stimulation with NaCN with and without pharmacological autonomic blockade; we also examined the cardiovascular regulation associated with air-breathing. As in most other air-breathing fish, air-breathing elicited a substantial tachycardia. This tachycardia was abolished by cholinergic muscarinic pharmacological blockade, which also abolished the cardiac limb of the baroreflex, and consequently such fish failed to maintain their arterial blood pressure when air-breathing. In higher vertebrate classes, baroreceptors elicit ventilatory changes; however, whether this is the case in fish has not previously been investigated. Pangasianodon hypophthalmus demonstrated a prominent increase in ventilation during imposed hypotension. Collectively, these results demonstrate, for the first time, an efficient baroreflex in an air-breathing fish, point towards involvement of baroreceptors in blood pressure regulation during air-breathing, and show a correlation between blood pressure and ventilation, providing additional information on the origin of this link.
- What determines the basal rate of metabolism? [Journal Article]
- JEJ Exp Biol 2019 Jul 01
- The basal rate of metabolism (BMR) is the most reported estimate of energy expenditure in endotherms. Its principal determinant is body mass, but it also correlates with a variety of behavioral not d…
The basal rate of metabolism (BMR) is the most reported estimate of energy expenditure in endotherms. Its principal determinant is body mass, but it also correlates with a variety of behavioral not determine basal rate, they are byproducts of the mechanisms that are its determinate. In mammals, mass-independent basal rate increases with muscle mass when it is>40% of body mass. Then basal rates in mammals are≥100% of the values expected from mass. Mammals with muscle masses<30% of body mass have lower basal rates, a diminished capacity to regulate body temperature, and often a reduced level of activity. At muscle masses<42% of body mass, birds have body temperatures and basal rates higher than mammals with the same muscle mass. Their high basal rates derive from a high blood flow and mitochondrial density in their pectoral muscles. These factors also occur in the flight muscles of bats. Oxygen transport to the pectoral muscles of birds is facilitated by an increase in heart mass and hematocrit. This arrangement avoids transporting a large muscle mass to fuel flight, thereby reducing the cost of flight. Pectoral muscle masses<9% of body mass correlate with a flightless condition in kiwis, rails, and ducks. Some fruit pigeons have basal rates as low as kiwis, while remaining volant. The mass-independent basal rates of endotherms principally reflect changes of muscle activity and mass. An increase in muscle mass may have contributed to the evolution of endothermy.
- Invited review: Development of acid-base regulation in vertebrates. [Review]
- CBComp Biochem Physiol A Mol Integr Physiol 2019 Jun 28; 236:110518
- Acid-base regulation at intra- and extracellular levels is of fundamental importance for developing animals, as it is for adults. Although adult animals exhibit well established acid-base regulatory …
Acid-base regulation at intra- and extracellular levels is of fundamental importance for developing animals, as it is for adults. Although adult animals exhibit well established acid-base regulatory capacities to offset acid-base disturbances, early developmental stages must develop some of the mechanisms to compensate for these disturbances. Thus, in this review we consider the multiple mechanisms that are involved in acid-base regulation in the early developmental stages of vertebrates. We start with a brief general review of the three basics mechanisms that adult animals use for acid-base regulation: 1) rapidly acting bicarbonate, phosphate and protein buffer systems; 2) respiratory elimination of metabolically produced CO2 with a time-course of minutes; and 3) excretion of HCO3- and H+ via gills, kidneys or other excretory organs, the slowest of the mechanisms with a time-course of hours or days. We then consider the ability of developing fishes, amphibians, reptiles and birds to regulate acid-base balance using these three mechanisms, as well as the timing of the onset of these various mechanisms during development. Overall, the ability to regulate acid-base balance in the face of environmental stressors becomes apparent early in developing vertebrates, especially when the early stages are free living (e.g. embryos in eggs) and have no parental support via placental structures. However, we still have only a poor understanding of the dynamics and actual partitioning of acid-base regulation between buffer systems, respiratory elimination of CO2, and urinary excretion of HCO3- and H+ excretion in developing or adult fishes, amphibians, reptiles and birds. Yet, such studies could help understand key questions ranging from the evolution of endothermy to the relative importance α-stat and pH-stat acid-base regulation.
- Sarcoplasmic reticulum Ca2+-ATPase (SERCA) activity during the transition to endothermy in an altricial bird. [Journal Article]
- JEJ Exp Biol 2019 Jun 28; 222(Pt 13)
- Sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a transmembrane pump critical to muscle calcium cycling during contraction, and SERCA has also been proposed as the basis for a non-shivering therm…
Sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a transmembrane pump critical to muscle calcium cycling during contraction, and SERCA has also been proposed as the basis for a non-shivering thermogenesis mechanism in birds. Despite its potential importance to both shivering and non-shivering thermogenesis, the activity of this transporter has rarely been studied in altricial birds, and never during the developmental transition from ectothermy to endothermy. Here, we describe SERCA activity in the pectoralis muscle and heart ventricle of red-winged blackbird (Agelaius phoeniceus) nestlings, fledglings and adults. Additionally, using a diet manipulation, we tested the hypothesis that muscle SERCA activity is affected by dietary fatty acid composition, as has been shown in some previous studies. In blackbird hearts, SERCA activity increased throughout development and into adulthood, conspicuously jumping higher just prior to fledging. In pectoralis muscle, SERCA activity increased throughout the nestling period, but then declined after fledging, an effect we attribute to remodeling of the muscle from a primarily heat-generating organ to a primarily force-generating organ. SERCA activity of the pectoralis muscle was correlated with the proportion of linoleic acid in muscle phospholipids when including all ages in the control group. However, in diet-manipulated birds, there was no consistent relationship between SERCA activity and muscle membrane fatty acid composition at any tested age (5-9 days old). It is unclear whether SERCA might be affected by developmental changes in fatty acid composition at younger ages.
- The Thermoregulatory Behavior of Nectar Foraging Polistine Wasps (Polistes dominula and Polistes gallicus) in Different Climate Conditions. [Journal Article]
- IInsects 2019 Jun 27; 10(7)
- Polistine wasps collect nectar for their energetic demand and for the provision of the brood. They are mainly ectothermic during different behavioral tasks. We investigated the body temperature of tw…
Polistine wasps collect nectar for their energetic demand and for the provision of the brood. They are mainly ectothermic during different behavioral tasks. We investigated the body temperature of two species living in differing habitats and climate regions, in order to reveal the environmental influence on their thermoregulatory behavior. The species were Polistes dominula in the temperate climate of Central Europe, and Polistes gallicus in the warm Mediterranean climate of Southern Europe. The wasp's body temperature was measured during foraging on lovage (Levisticum officinale) and fennel (Foeniculum vulgare) by infrared thermography in the entire ambient temperature range they are usually exposed to (Ta ~ 20-40 °C). The temperature of all body parts increased nearly linearly with ambient temperature, with the thorax as the warmest part. To achieve optimal foraging temperatures, they preferably use solar radiation. An "operative temperature model" enabled the evaluation of the endothermic effort. Polistes dominula foraging on lovage exhibited no endothermic activity. However, while foraging on fennel they had a weak and almost constant endothermic performance of about 1 °C. Polistes gallicus, by contrast, exhibited mostly no or only minor endothermy during foraging. Both wasps avoid a high energetic effort and this way reduce their foraging costs.
- The Early Origin of Feathers. [Review]
- TETrends Ecol Evol 2019 Jun 01
- Feathers have long been regarded as the innovation that drove the success of birds. However, feathers have been reported from close dinosaurian relatives of birds, and now from ornithischian dinosaur…
Feathers have long been regarded as the innovation that drove the success of birds. However, feathers have been reported from close dinosaurian relatives of birds, and now from ornithischian dinosaurs and pterosaurs, the cousins of dinosaurs. Incomplete preservation makes these reports controversial. If true, these findings shift the origin of feathers back 80 million years before the origin of birds. Gene regulatory networks show the deep homology of scales, feathers, and hairs. Hair and feathers likely evolved in the Early Triassic ancestors of mammals and birds, at a time when synapsids and archosaurs show independent evidence of higher metabolic rates (erect gait and endothermy), as part of a major resetting of terrestrial ecosystems following the devastating end-Permian mass extinction.
- Reappraising the exteriorization of the mammalian testes through evolutionary physiology. [Review]
- CICommun Integr Biol 2019; 12(1):38-54
- A number of theories have been proposed to explain the exteriorization of the testicles in most mammalian species. None of these provide a consistent account for the wide variety of testicular locati…
A number of theories have been proposed to explain the exteriorization of the testicles in most mammalian species. None of these provide a consistent account for the wide variety of testicular locations found across the animal kingdom. It is proposed that testicular location is the result of coordinate action of testicular tissue ecologies to sustain preferential states of homeostatic equipoise throughout evolutionary development in response to the advent of endothermy.
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- A Brief Introduction to Methods for Describing Body Temperature in Endotherms. [Journal Article]
- PBPhysiol Biochem Zool 2019 Jul/Aug; 92(4):365-372
- Researchers commonly measure body, orifice, or skin temperature (collectively referred to as body temperature [Tb] herein) of endothermic animals in biomedical, physiological, evolutionary, and ecolo…
Researchers commonly measure body, orifice, or skin temperature (collectively referred to as body temperature [Tb] herein) of endothermic animals in biomedical, physiological, evolutionary, and ecological studies. However, comparing Tb among species or placing a single study in context is challenging because there is no single, standard method to describe and synthesize Tb data of endotherms. A variety of metrics are available, and each has strengths and weaknesses appropriate for answering different types of questions. Importantly, choosing the wrong metric to address the question posed can lead to misinterpretations and misleading presentation of Tb data. Here I review standard metrics used to describe central tendencies and variation in Tb of endothermic species, focusing on important strengths and weaknesses and suggested questions to be addressed using each metric. One of the most common mistakes in analyzing Tb data is mismatching the analytical metric and the question being asked, so, ultimately, individual researchers need to determine which is most appropriate for addressing their question based on the implications of using each metric.