A. Dittmar

Bio: A. Dittmar is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Thermogenesis & Glucagon. The author has an hindex of 2, co-authored 2 publications receiving 109 citations.

Potentiated muscular thermogenesis in cold-acclimated muscovy duckling

Abstract: The capacity for nonshivering thermogenesis (NST) was examined in 26- to 27-day cold-acclimated (CA) muscovy ducklings reared for 21 days at 4 degrees C. Metabolic rate and integrated electromyographic (EMG) muscle activity were measured at ambient temperature ranging from -10 to 28 degrees C. Compared with controls reared at 30 degrees C, CA ducklings were more resistant to cold and had higher peak metabolic rate in extreme cold. Shivering threshold temperature of CA ducklings was 14.2 degrees C lower than lower critical temperature, whereas for controls the two temperatures were similar. Thus CA ducklings exhibited an NST in moderate cold. In addition, at temperatures that produced shivering, EMG activity in CA duckling muscle was lesser than that of controls, even at a higher metabolic rate. Because these ducklings are devoid of brown adipose tissue, these results indicated an increased thermogenic efficiency of muscular activity in CA ducklings.

Increased role of skeletal muscle in the calorigenic response to glucagon of cold-acclimated ducklings.

Abstract: The site of the calorigenesis observed in birds after glucagon was sought in control and cold-acclimated (CA) ducklings. Twenty-four 6-wk-old muscovy ducklings were reared either at thermoneutrality (TN) (25 degrees C) or in the cold (4 degrees C) from the age of 1 wk. Glucagon-induced calorigenesis (GIC) was estimated at 25 degrees C after a peritoneal glucagon injection (103 nmol/kg). Glucagon induced a higher increase in animal heat production (indirect calorimetry) and body temperature in CA (+45% and +1.1 degrees C) than in control ducklings (+30% and +0.4 degree C). In CA ducklings, the perfusion rate (thermal clearance method) and temperature of gastrocnemius increased (+130% and +1.0 degree C) shortly after glucagon, whereas tissue oxygenation (polarography) decreased (-34%). There was no significant effect of glucagon in TN controls. These changes, which peaked 45-60 min after glucagon injection, indicated a prolonged increase of muscle O2 consumption in CA ducklings. Leg muscle blood flow (radioactive microspheres) measured 45 min after glucagon was slightly increased in controls (+20%; P < 0.05), while in CA ducklings, the increase was larger (+76%; P < 0.05). The arteriovenous difference in O2 content was not markedly affected by glucagon in both groups. These parameters indicated an increase in leg muscle O2 uptake in response to glucagon of +29% in controls and +76% in CA ducklings. In controls, 28% of the GIC measured in vivo could be attributed to whole body skeletal muscles, compared with 53% in CA ducklings. The remaining part might be accounted for mostly by the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermogenic mechanisms and their hormonal regulation.

Abstract: Increased heat generation from biological processes is inherent to homeothermy. Homeothermic species produce more heat from sustaining a more active metabolism as well as from reducing fuel efficie...

The role of skeletal-muscle-based thermogenic mechanisms in vertebrate endothermy

Abstract: Thermogenesis is one of the most important homeostatic mechanisms that evolved during vertebrate evolution. Despite its importance for the survival of the organism, the mechanistic details behind various thermogenic processes remain incompletely understood. Although heat production from muscle has long been recognized as a thermogenic mechanism, whether muscle can produce heat independently of contraction remains controversial. Studies in birds and mammals suggest that skeletal muscle can be an important site of non-shivering thermogenesis (NST) and can be recruited during cold adaptation, although unequivocal evidence is lacking. Much research on thermogenesis during the last two decades has been focused on brown adipose tissue (BAT). These studies clearly implicate BAT as an important site of NST in mammals, in particular in newborns and rodents. However, BAT is either absent, as in birds and pigs, or is only a minor component, as in adult large mammals including humans, bringing into question the BAT-centric view of thermogenesis. This review focuses on the evolution and emergence of various thermogenic mechanisms in vertebrates from fish to man. A careful analysis of the existing data reveals that muscle was the earliest facultative thermogenic organ to emerge in vertebrates, long before the appearance of BAT in eutherian mammals. Additionally, these studies suggest that muscle-based thermogenesis is the dominant mechanism of heat production in many species including birds, marsupials, and certain mammals where BAT-mediated thermogenesis is absent or limited. We discuss the relevance of our recent findings showing that uncoupling of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) by sarcolipin (SLN), resulting in futile cycling and increased heat production, could be the basis for NST in skeletal muscle. The overall goal of this review is to highlight the role of skeletal muscle as a thermogenic organ and provide a balanced view of thermogenesis in vertebrates.

Avian Adjustments to Cold

Abstract: For birds that breed in areas with severe winters, latitudinal and/or altitudinal migration provides the possibility of moving to places where cold and inclement weather and associated difficulties of food procurement are less challenging. Nevertheless, a substantial number of species do not use this option and so must contend with these problems. The responses of birds to cold have been studied extensively over the past 4 decades and reviewed repeatedly within more general accounts of avian thermoregulation (Whittow 1986), as part of monographs on individual species (Rautenberg 1983), or in connection with analysis of particular facets of avian cold defense (Dawson et al. 1983 b; Marsh and Dawson 1989). The contribution of Calder and King (1974) has proved particularly useful, for, in addition to providing a rigorous review of avian responses to heat and cold, it includes an extensive series of allometric equations describing the mass dependence of energetic and thermoregulatory functions. With so many reviews available, an additional treatment of the subject might appear superfluous. However, new findings are being published at unprecedented rates and allow for an effective integration of various behavioral and physiological tactics used in cold defense.