Limits to sustained energy intake VIII: Resting metabolic rate and organ morphology of laboratory mice lactating at thermoneutralith

Research output: Contribution to journalArticle

83 Citations (Scopus)

Abstract

We have previously shown that the food intake and milk production of MF1 laboratory mice lactating at 30degreesC, 21degreesC and 8degreesC increase as temperature declines. These data suggest that mice are not limited peripherally by the capacity of the mammary glands to produce milk but are limited by the capacity of the animal to dissipate body heat generated as a by-product of food processing and milk production. Here, we measure resting metabolic rate (RMR; prior to breeding and at peak lactation) and organ morphology (at peak lactation) in MF1 mice exposed to 30degreesC (thermoneutrality) and compare these traits with the same parameters measured previously in mice at 21degreesC and 8degreesC. The masses of visceral organs primarily responsible for energy flux (heart, lungs, stomach, small intestine, large intestine, liver, pancreas, spleen and kidneys) increased as temperature declined. The masses of all these organ differed between mice exposed to 8degreesC and 21degreesC, whereas only the masses of heart, liver and kidneys differed between mice at 21degreesC and 30degreesC. The increases in organ masses were paralleled by increases in RMR at peak lactation above the levels measured prior to breeding, with mice at 8degreesC and 21degreesC having significantly higher increases in RMR than mice at 30degreesC (29.6 kJ day(-1), 25.5 kJ day(-1) and 8.1 kJ day(-1), respectively). The observed changes in visceral organs and RMR are consistent with both the heat dissipation and peripheral limit hypotheses. However, mice exposed to 8degreesC had substantially larger mammary glands than mice at 21degreesC or 30degreesC (2.450 g, 1.115 g and 0.956 g dry mass, respectively), which argues against the peripheral limitation hypothesis and is consistent with the heat dissipation limit hypothesis. In addition, cold exposure resulted in greater masses of brown adipose tissue, white adipose tissue, pelage and tail. We discuss these changes in the context of the potential thermoregulatory benefits from use of the heat generated as a by-product of milk synthesis.

Original languageEnglish
Pages (from-to)4283-4291
Number of pages8
JournalJournal of Experimental Biology
Volume206
Issue number23
DOIs
Publication statusPublished - 2003

Keywords

  • resting metabolic rate
  • organ morphology
  • peripheral limit
  • heat dissipation limit
  • laboratory mouse
  • Mus musculus
  • BROWN ADIPOSE-TISSUE
  • MUS MUSCULUS
  • PEROMYSCUS-MANICULATUS
  • DEER MICE
  • INTRASPECIFIC VARIATION
  • CONCURRENT PREGNANCY
  • INDIVIDUAL VARIATION
  • SIGMODON-HISPIDUS
  • COLD-EXPOSURE
  • FOOD-INTAKE

Cite this

@article{a941cf9d25d24925b3e1950c83bde1b8,
title = "Limits to sustained energy intake VIII: Resting metabolic rate and organ morphology of laboratory mice lactating at thermoneutralith",
abstract = "We have previously shown that the food intake and milk production of MF1 laboratory mice lactating at 30degreesC, 21degreesC and 8degreesC increase as temperature declines. These data suggest that mice are not limited peripherally by the capacity of the mammary glands to produce milk but are limited by the capacity of the animal to dissipate body heat generated as a by-product of food processing and milk production. Here, we measure resting metabolic rate (RMR; prior to breeding and at peak lactation) and organ morphology (at peak lactation) in MF1 mice exposed to 30degreesC (thermoneutrality) and compare these traits with the same parameters measured previously in mice at 21degreesC and 8degreesC. The masses of visceral organs primarily responsible for energy flux (heart, lungs, stomach, small intestine, large intestine, liver, pancreas, spleen and kidneys) increased as temperature declined. The masses of all these organ differed between mice exposed to 8degreesC and 21degreesC, whereas only the masses of heart, liver and kidneys differed between mice at 21degreesC and 30degreesC. The increases in organ masses were paralleled by increases in RMR at peak lactation above the levels measured prior to breeding, with mice at 8degreesC and 21degreesC having significantly higher increases in RMR than mice at 30degreesC (29.6 kJ day(-1), 25.5 kJ day(-1) and 8.1 kJ day(-1), respectively). The observed changes in visceral organs and RMR are consistent with both the heat dissipation and peripheral limit hypotheses. However, mice exposed to 8degreesC had substantially larger mammary glands than mice at 21degreesC or 30degreesC (2.450 g, 1.115 g and 0.956 g dry mass, respectively), which argues against the peripheral limitation hypothesis and is consistent with the heat dissipation limit hypothesis. In addition, cold exposure resulted in greater masses of brown adipose tissue, white adipose tissue, pelage and tail. We discuss these changes in the context of the potential thermoregulatory benefits from use of the heat generated as a by-product of milk synthesis.",
keywords = "resting metabolic rate, organ morphology, peripheral limit, heat dissipation limit, laboratory mouse, Mus musculus, BROWN ADIPOSE-TISSUE, MUS MUSCULUS, PEROMYSCUS-MANICULATUS, DEER MICE, INTRASPECIFIC VARIATION, CONCURRENT PREGNANCY, INDIVIDUAL VARIATION, SIGMODON-HISPIDUS, COLD-EXPOSURE, FOOD-INTAKE",
author = "Krol, {Elzbieta Barbara} and Speakman, {John Roger}",
year = "2003",
doi = "10.1242/jeb.00676",
language = "English",
volume = "206",
pages = "4283--4291",
journal = "Journal of Experimental Biology",
issn = "0022-0949",
publisher = "Company of Biologists Ltd",
number = "23",

}

TY - JOUR

T1 - Limits to sustained energy intake VIII: Resting metabolic rate and organ morphology of laboratory mice lactating at thermoneutralith

AU - Krol, Elzbieta Barbara

AU - Speakman, John Roger

PY - 2003

Y1 - 2003

N2 - We have previously shown that the food intake and milk production of MF1 laboratory mice lactating at 30degreesC, 21degreesC and 8degreesC increase as temperature declines. These data suggest that mice are not limited peripherally by the capacity of the mammary glands to produce milk but are limited by the capacity of the animal to dissipate body heat generated as a by-product of food processing and milk production. Here, we measure resting metabolic rate (RMR; prior to breeding and at peak lactation) and organ morphology (at peak lactation) in MF1 mice exposed to 30degreesC (thermoneutrality) and compare these traits with the same parameters measured previously in mice at 21degreesC and 8degreesC. The masses of visceral organs primarily responsible for energy flux (heart, lungs, stomach, small intestine, large intestine, liver, pancreas, spleen and kidneys) increased as temperature declined. The masses of all these organ differed between mice exposed to 8degreesC and 21degreesC, whereas only the masses of heart, liver and kidneys differed between mice at 21degreesC and 30degreesC. The increases in organ masses were paralleled by increases in RMR at peak lactation above the levels measured prior to breeding, with mice at 8degreesC and 21degreesC having significantly higher increases in RMR than mice at 30degreesC (29.6 kJ day(-1), 25.5 kJ day(-1) and 8.1 kJ day(-1), respectively). The observed changes in visceral organs and RMR are consistent with both the heat dissipation and peripheral limit hypotheses. However, mice exposed to 8degreesC had substantially larger mammary glands than mice at 21degreesC or 30degreesC (2.450 g, 1.115 g and 0.956 g dry mass, respectively), which argues against the peripheral limitation hypothesis and is consistent with the heat dissipation limit hypothesis. In addition, cold exposure resulted in greater masses of brown adipose tissue, white adipose tissue, pelage and tail. We discuss these changes in the context of the potential thermoregulatory benefits from use of the heat generated as a by-product of milk synthesis.

AB - We have previously shown that the food intake and milk production of MF1 laboratory mice lactating at 30degreesC, 21degreesC and 8degreesC increase as temperature declines. These data suggest that mice are not limited peripherally by the capacity of the mammary glands to produce milk but are limited by the capacity of the animal to dissipate body heat generated as a by-product of food processing and milk production. Here, we measure resting metabolic rate (RMR; prior to breeding and at peak lactation) and organ morphology (at peak lactation) in MF1 mice exposed to 30degreesC (thermoneutrality) and compare these traits with the same parameters measured previously in mice at 21degreesC and 8degreesC. The masses of visceral organs primarily responsible for energy flux (heart, lungs, stomach, small intestine, large intestine, liver, pancreas, spleen and kidneys) increased as temperature declined. The masses of all these organ differed between mice exposed to 8degreesC and 21degreesC, whereas only the masses of heart, liver and kidneys differed between mice at 21degreesC and 30degreesC. The increases in organ masses were paralleled by increases in RMR at peak lactation above the levels measured prior to breeding, with mice at 8degreesC and 21degreesC having significantly higher increases in RMR than mice at 30degreesC (29.6 kJ day(-1), 25.5 kJ day(-1) and 8.1 kJ day(-1), respectively). The observed changes in visceral organs and RMR are consistent with both the heat dissipation and peripheral limit hypotheses. However, mice exposed to 8degreesC had substantially larger mammary glands than mice at 21degreesC or 30degreesC (2.450 g, 1.115 g and 0.956 g dry mass, respectively), which argues against the peripheral limitation hypothesis and is consistent with the heat dissipation limit hypothesis. In addition, cold exposure resulted in greater masses of brown adipose tissue, white adipose tissue, pelage and tail. We discuss these changes in the context of the potential thermoregulatory benefits from use of the heat generated as a by-product of milk synthesis.

KW - resting metabolic rate

KW - organ morphology

KW - peripheral limit

KW - heat dissipation limit

KW - laboratory mouse

KW - Mus musculus

KW - BROWN ADIPOSE-TISSUE

KW - MUS MUSCULUS

KW - PEROMYSCUS-MANICULATUS

KW - DEER MICE

KW - INTRASPECIFIC VARIATION

KW - CONCURRENT PREGNANCY

KW - INDIVIDUAL VARIATION

KW - SIGMODON-HISPIDUS

KW - COLD-EXPOSURE

KW - FOOD-INTAKE

U2 - 10.1242/jeb.00676

DO - 10.1242/jeb.00676

M3 - Article

VL - 206

SP - 4283

EP - 4291

JO - Journal of Experimental Biology

JF - Journal of Experimental Biology

SN - 0022-0949

IS - 23

ER -