Limits to sustained energy intake IX: a review of hypotheses

Abstract

Several lines of evidence indicate that animals in the wild may be limited in their maximal rates of energy intake by their intrinsic physiology rather than food availability. Understanding the limits to sustained energy intake is important because this defines an envelope within which animals must trade-off competing activities. In the first part of this review, we consider the initial ideas that propelled this area and experimental evidence connected with them. An early conceptual advance in this field was the idea that energy intake could be centrally limited by aspects of the digestive process, or peripherally limited at the sites of energy utilisation. A model system that has been widely employed to explore these ideas is lactation in small rodents. Initial studies in the late 1980s indicated that energy intake might be centrally limited, but work by Hammond and colleagues in the 1990s suggested that it was more likely that the limits were imposed by capacity of the mammary glands, and other works tended to support this view. This consensus, however, was undermined by studies that showed milk production was higher in mice at low temperatures, suggesting that the capacity of the mammary gland is not a limiting factor. In the second part of the review we consider some additional hypotheses that might explain these conflicting data. These include the heat dissipation limits hypothesis, the seasonal investment hypothesis and the saturated neural control hypothesis. Current evidence with respect to these hypotheses is also reviewed. The limited evidence presently available does not unambiguously support any one of them.

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Abbreviations

α-MSH:

Alpha-melanocyte stimulating hormone

AgRP:

Agouti-related peptide

ARC:

Arcuate nucleus of the hypothalamus

BAT:

Brown adipose tissue

CART:

Cocaine- and amphetamine-regulated transcript

db/db :

Obese diabetic mouse

MC3R, MC4R:

melanocortin-3 and -4 receptors

MTII:

A receptor agonist for MC3R and MC4R

NPY:

Neuropeptide Y

ob/ob:

Obese mutant mouse

Ob-Ra, Ob-Rb.....Ob-Rf:

Leptin receptor sub-types a to f

POMC:

Pro-opiomelanocortin

PRL:

Prolactin

PrRP:

Prolactin-releasing peptide

PVN:

Paraventricular nucleus of the hypothalamus

SusEI:

Sustained energy intake

SusMR:

Sustained metabolic rate

TRH:

Thyrotropin-releasing hormone

UCP-1.....UCP-5:

Uncoupling proteins 1, 2, 3, 4 and 5

Y1:

Receptor for neuropeptide Y

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Acknowledgements

Our work on energetics of lactation and SusEI has been funded by the UK Biotechnology and Biological Sciences Research Council. We are grateful to the numerous honours students that have worked on these projects and to Peter Thomson and the staff of the animal house facility at the University of Aberdeen for their invaluable technical support. Julian Mercer, Ian Hume and two anonymous referees made valuable comments on earlier drafts of the manuscript.

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Limits to sustained energy intake VIII: Król et al. (2003) J Exp Biol 206:4283-4291.

Communicated by I.D. Hume

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Speakman, J.R., Król, E. Limits to sustained energy intake IX: a review of hypotheses. J Comp Physiol B 175, 375–394 (2005). https://doi.org/10.1007/s00360-005-0013-3

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Keywords

  • Sustained energy intake
  • Food intake
  • Energy expenditure
  • Heat dissipation
  • Mammary gland
  • Lactation
  • Neuropeptides
  • Hypothalamus
  • Brown adipose tissue
  • Leptin
  • Prolactin