Physiological Mechanisms in the Adaptive Response of Metabolic Rates to Energy Restriction

Ps, Shetty

doi:10.1079/nrr19900006

Cited by 60 publications

(38 citation statements)

References 116 publications

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“…Penguins tolerate during diving a decrease of T c (measured in the abdomen) to save energy and to extend their aerobic dive limit (5,11,25). A decrease of BMR is also a common response to water deprivation (61), food restriction and starvation (12,15,64,65), or low ambient temperatures (41). However, such reactions apparently do not indicate impaired thermoregulation but seem to be well-regulated adaptive extensions of adjustments normally occurring during sleep and circadian rhythmicity (24,52,64).…”

Section: Annual Changes Of Mrs and Underlying Causesmentioning

confidence: 99%

Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus)

Arnold

Ruf

Reimoser

et al. 2004

American Journal of Physiology-Regulatory, Integrative and Comp

128

143

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. Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus). Am J Physiol Regul Integr Comp Physiol 286: R174-R181, 2004. First published September 11, 2003 10.1152/ajpregu.00593.2002Herbivores of temperate and arctic zones are confronted during winter with harsh climatic conditions and nutritional shortness. It is still not fully understood how large ungulates cope with this twofold challenge. We found that red deer, similar to many other northern ungulates, show large seasonal fluctuations of metabolic rate, as indicated by heart rate, with a 60% reduction at the winter nadir compared with the summer peak. A previously unknown mechanism of energy conservation, i.e., nocturnal hypometabolism associated with peripheral cooling, contributed significantly to lower energy expenditure during winter. Predominantly during late winter night and early morning hours, subcutaneous temperature could decrease substantially. Importantly, during these episodes of peripheral cooling, heart rate was not maintained at a constant level, as to be expected from classical models of thermoregulation in the thermoneutral zone, but continuously decreased with subcutaneous temperature, both during locomotor activity and at rest. This indicates that the circadian minimum of basal metabolic rate and of the set-point of body temperature regulation varied and dropped to particularly low levels during late winter. Our results suggest, together with accumulating evidence from other species, that reducing endogenous heat production is not restricted to hibernators and daily heterotherms but is a common and well-regulated physiological response of endothermic organisms to energetically challenging situations. Whether the temperature of all tissues is affected, or the body shell only, may simply be a result of the duration and degree of hypometabolism and its interaction with body size-dependent heat loss. hypometabolism; hypothermia; winter adaptation; body temperature regulation MANY UNGULATES ARE CAPABLE of withstanding long and cold winters with low food availability. Large body size, excellent fur insulation, and countercurrent heat exchange mechanisms contribute to minimize energy requirements under cold load. However, reduced heat loss alone can hardly explain the substantially lowered metabolic rate (MR) of northern ungulates and the apparently ubiquitous decrease of voluntary food intake during winter (4,13,18,28,35,37,42,44,59,63,72). The search for mechanism to explain reduced energy expenditure during winter has so far produced equivocal results. Studies on white-tailed deer [Odocoileus virginianus (66)], moose [Alces alces (56, 57)], roe deer [Capreolus capreolus (69)], and wapiti [Cervus elaphus nelsoni (49)] reported that animals had reduced MRs during winter. However, other studies failed to find any differences between summer and winter basal metabolic rate (BMR) and concluded that seasonal variations in MR were merely consequences of different activity levels and failures to measure animals within thei...

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Section: Annual Changes Of Mrs and Underlying Causesmentioning

confidence: 99%

Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus)

Arnold

Ruf

Reimoser

et al. 2004

American Journal of Physiology-Regulatory, Integrative and Comp

128

143

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“…Treatment with leptin partly prevented the fall in serum T 4 on fasting (Ahima 2000). Thyroid hormones increase basal metabolic rate (Shetty 1990) and may also enhance brown adipose tissue thermogenesis (Silva 1993). Undernutrition results in decreased energy expenditure, which is at least partly due to the concomitant hypothyroidism (Shetty 1990).…”

Section: Leptin and Tmentioning

confidence: 99%

“…Thyroid hormones increase basal metabolic rate (Shetty 1990) and may also enhance brown adipose tissue thermogenesis (Silva 1993). Undernutrition results in decreased energy expenditure, which is at least partly due to the concomitant hypothyroidism (Shetty 1990). Thus the hypoleptinaemia of lactation could contribute to the hypothyroidism, and hence increased metabolic efficiency of the state.…”

Section: Leptin and Tmentioning

confidence: 99%

Regulation of serum leptin and its role in the hyperphagia of lactation in the rat

Denis¹,

Williams²,

Vernon³

2003

Journal of Endocrinology

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The factors regulating serum leptin concentration and its relationship to the hyperphagia of lactation have been investigated in rats. Lactation results in hypoleptinaemia and loss, or at least marked attenuation, of the nocturnal rise in serum leptin. Litter removal resulted in a fall in food intake and restoration of the nocturnal rise in serum leptin. Returning the litter to the mother after a 48-h absence increased food intake and began to reinitiate milk production, but the nocturnal serum leptin levels were still increased at 48 h after litter restoration. Adjusting litter size to four, eight, ten or fourteen pups at parturition resulted in different rates of litter growth and food intake during the subsequent lactation, but had no effect on the degree of hypoleptinaemia. Reducing litter size from ten to four pups at mid-lactation resulted in a transient increase in both serum leptin and pup growth rate, while food intake fell to a level found in rats suckling four pups throughout lactation. Reducing milk production by injection of bromocriptine increased serum leptin, but did not restore the nocturnal rise in serum leptin; food intake decreased, but remained much higher than in nonlactating rats. Feeding a varied, high-energy diet resulted in a decrease in the weight of food ingested, but no change in calorie intake, and had no effect on the hypoleptinaemia. These studies suggested that the hypoleptinaemia of lactating rats is due to negative energy balance, but the loss of the nocturnal rise in serum leptin is due to the suckling stimulus. The negative energy balance of lactation does not appear to be caused by a physical constraint on food intake. While the hypoleptinaemia should facilitate the hyperphagia of lactation, other orexigenic signals must also be involved.

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“…Adaptations to low energy intakes PS Shetty S17 process and have been summarised recently (Shetty, 1990). Since the reduction in this component is manifest in the early phase of semi-starvation the related physiological mechanisms must be apparent during the ®rst 2 ± 3 weeks of energy restriction and are likely to be endocrine in nature.…”

Section: Basal Metabolic Ratesmentioning

confidence: 99%

Adaptation to low energy intakes: the responses and limits to low intakes in infants, children and adults

1999

Eur J Clin Nutr

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Reduction in energy intake below the acceptable level of requirement for an individual results in a series of physiological and behavioural responses, which are considered as an adaptation to the low energy intake. This ability of the human body to adapt to a lowering of the energy intake is without doubt bene®cial to the survival of the individual. However, what is more controversial is the view held by some that the body can metabolically adapt in a bene®cial manner to a lowered intake and consequently that the requirements for energy are variable given the same body size and composition and physical activity levels. Much of this confusion is the result of considerable evidence from studies conducted in well-nourished adults who, for experimental or other reasons, have lowered their intakes and consequently demonstrated an apparently enhanced metabolic ef®ciency resulting from changes in metabolic rates which are disproportionate to the changes in body weight. Similar increases in metabolic ef®ciency are not readily seen in individuals who on long-term marginal intakes, probably from childhood, have developed into short-statured, low-body-weight adults with a different body composition. It would thus appear that the generally used indicator of metabolic ef®ciency in humans, that is a reduced oxygen consumption per unit fat free mass, is fraught with problems since it does not account for variations in contributions from sub-compartments of the fat free mass which include those with high metabolism at rest such as brain and viscera and those with low metabolism at rest such as muscle mass. Metabolic rate per unit fat free mass thus, does not re¯ect true variations in metabolic ef®ciency and is due largely to variations in body composition. This ®nding combined with the evidence that behavioural adaptation in habitual physical activity patterns which occurs on energy restriction is not necessarily bene®cial to the individual raises doubts about the role of adaptation to low intakes in determining one's requirement for energy. The evidence is overwhelming that both in children and adults, changes in body size and composition as well as in levels of habitual physical activity may be the most important consequences of a lowered energy intake and cannot be assumed to be a part of a bene®cial adaptation that in¯uences energy requirements.

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Physiological Mechanisms in the Adaptive Response of Metabolic Rates to Energy Restriction

Cited by 60 publications

References 116 publications

Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus)

Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus)

Regulation of serum leptin and its role in the hyperphagia of lactation in the rat

Adaptation to low energy intakes: the responses and limits to low intakes in infants, children and adults

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