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Yang R, Cao J, Speakman JR, Zhao Z. Limits to sustained energy intake. XXXIII. Thyroid hormones play important roles in milk production but do not define the heat dissipation limit in Swiss mice. J Exp Biol 2023; 226:jeb245393. [PMID: 37767758 DOI: 10.1242/jeb.245393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Accepted: 09/22/2023] [Indexed: 09/29/2023]
Abstract
The limits to sustained energy intake set physiological upper boundaries that affect many aspects of human and animal performance. The mechanisms underlying these limits, however, remain unclear. We exposed Swiss mice to either supplementary thyroid hormones (THs) or the inhibitor methimazole during lactation at 21 or 32.5°C, and measured food intake, resting metabolic rate (RMR), milk energy output (MEO), serum THs and mammary gland gene expression of females, and litter size and mass of their offspring. Lactating females developed hyperthyroidism following exposure to supplementary THs at 21°C, but they did not significantly change body temperature, asymptotic food intake, RMR or MEO, and litter and mass were unaffected. Hypothyroidism, induced by either methimazole or 32.5°C exposure, significantly decreased asymptotic food intake, RMR and MEO, resulting in significantly decreased litter size and litter mass. Furthermore, gene expression of key genes in the mammary gland was significantly decreased by either methimazole or heat exposure, including gene expression of THs and prolactin receptors, and Stat5a and Stat5b. This suggests that endogenous THs are necessary to maintain sustained energy intake and MEO. Suppression of the thyroid axis seems to be an essential aspect of the mechanism by which mice at 32.5°C reduce their lactation performance to avoid overheating. However, THs do not define the upper limit to sustained energy intake and MEO at peak lactation at 21°C. Another, as yet unknown, factor prevents supplementary thyroxine exerting any stimulatory metabolic impacts on lactating mice at 21°C.
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Affiliation(s)
- Rui Yang
- College of Life and Environmental Science, Zhejiang Provincial Key Laboratory for Water Environment and Marine Biological Resources Protection, Wenzhou University, Wenzhou 325035, China
| | - Jing Cao
- College of Life and Environmental Science, Zhejiang Provincial Key Laboratory for Water Environment and Marine Biological Resources Protection, Wenzhou University, Wenzhou 325035, China
| | - John R Speakman
- Shenzhen Key Laboratory of Metabolic Health, Center for Energy Metabolism and Reproduction, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
- Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK
| | - Zhijun Zhao
- College of Life and Environmental Science, Zhejiang Provincial Key Laboratory for Water Environment and Marine Biological Resources Protection, Wenzhou University, Wenzhou 325035, China
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Hyatt HW, Zhang Y, Hood WR, Kavazis AN. Changes in Metabolism, Mitochondrial Function, and Oxidative Stress Between Female Rats Under Nonreproductive and 3 Reproductive Conditions. Reprod Sci 2018; 26:114-127. [PMID: 29621953 DOI: 10.1177/1933719118766264] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Women who do not lactate display increased incidence of obesity, type II diabetes, and cancer. Stuebe and Rich-Edwards proposed that these effects occur because physiological changes that ensue during pregnancy are not reversed without lactation. To empirically test this hypothesis, we compared markers of metabolism, mitochondrial function, and oxidative stress between 4 groups of Sprague-Dawley rats: (1) nonreproductive (NR) rats, (2) rats killed at day 20 of gestation, (3) rats that gave birth but were not allowed to suckle their pups (nonlactating), and (4) rats that suckled their young for 14 days. Nonlactating females displayed higher body fat compared to all other groups. Peroxisome proliferator-activated receptor δ (PPARδ) in skeletal muscle and white adipose tissue of nonlactating rats was lower than the other groups. The PPARδ is associated with lipid metabolism suggesting that the higher fat mass in nonlactating females was not associated with the retention of a physiological state that was set during pregnancy but instead an independent drop in PPARδ. Relative mitochondrial respiratory function and complex activity in the liver and skeletal muscle of nonlactating mice were not predictive of higher body mass, and measures of oxidative stress displayed minimal variation between groups.
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Affiliation(s)
- Hayden W Hyatt
- 1 School of Kinesiology, Auburn University, Auburn, AL, USA
| | - Yufeng Zhang
- 2 Department of Biological Sciences, Auburn University, Auburn, AL, USA
| | - Wendy R Hood
- 2 Department of Biological Sciences, Auburn University, Auburn, AL, USA
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Wen J, Tan S, Qiao QG, Fan WJ, Huang YX, Cao J, Liu JS, Wang ZX, Zhao ZJ. Sustained energy intake in lactating Swiss mice: a dual modulation process. J Exp Biol 2017; 220:2277-2286. [DOI: 10.1242/jeb.157107] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Accepted: 04/04/2017] [Indexed: 12/15/2022]
Abstract
Limits to sustained energy intake (SusEI) during lactation are important because they provide an upper boundary below which females must trade-off competing physiological activities. To date, SusEI is thought to be limited either by the capacity of the mammary glands to produce milk (the peripheral limitation hypothesis), or by a female's ability to dissipate body heat (the heat dissipation hypothesis). In the present study, we examined the effects of litter size and ambient temperature on a set of physiological, behavioral, and morphological indicators of SusEI and reproductive performance in lactating Swiss mice. Our results indicate that energy input, output, and mammary gland mass increased with litter size, whereas pup body mass and survival rate decreased. The body temperature increased significantly, while food intake (18g/d at 21°C vs 10g/d at 30°C), thermal conductance (lower by 20-27% at 30°C than 21°C), litter mass and MEO decreased significantly in the females raising large litter size at 30°C compared to those at 21°C. Furthermore, an interaction between ambient temperature and litter size affected females' energy budget, imposing strong constraints on SusEI. Together, out data suggest that the limitation may be caused by both mammary glands and heat dissipation, i.e. the limits to mammary gland is dominant at the room temperature, but heat limitation is more significant at warm temperatures. Further, the level of heat dissipation limits may be temperature dependent, shifting down with increasing temperature.
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Affiliation(s)
- Jing Wen
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
| | - Song Tan
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
| | - Qing-Gang Qiao
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
| | - Wei-Jia Fan
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
| | - Yi-Xin Huang
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
| | - Jing Cao
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
| | - Jin-Song Liu
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
| | - Zuo-Xin Wang
- Department of Psychology and Program in Neuroscience, Florida State University, Tallahassee, FL 32306-1270, USA
| | - Zhi-Jun Zhao
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, China
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Jothery AHA, Vaanholt LM, Mody N, Arnous A, Lykkesfeldt J, Bünger L, Hill WG, Mitchell SE, Allison DB, Speakman JR. Oxidative costs of reproduction in mouse strains selected for different levels of food intake and which differ in reproductive performance. Sci Rep 2016; 6:36353. [PMID: 27841266 PMCID: PMC5107891 DOI: 10.1038/srep36353] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 09/29/2016] [Indexed: 12/24/2022] Open
Abstract
Oxidative damage caused by reactive oxygen species has been hypothesised to underpin the trade-off between reproduction and somatic maintenance, i.e., the life-history-oxidative stress theory. Previous tests of this hypothesis have proved equivocal, and it has been suggested that the variation in responses may be related to the tissues measured. Here, we measured oxidative damage (protein carbonyls, 8-OHdG) and antioxidant protection (enzymatic antioxidant activity and serum antioxidant capacity) in multiple tissues of reproductive (R) and non-reproductive (N) mice from two mouse strains selectively bred for high (H) or low (L) food intake, which differ in their reproductive performance, i.e., H mice have increased milk energy output (MEO) and wean larger pups. Levels of oxidative damage were unchanged (liver) or reduced (brain and serum) in R versus N mice, and no differences in multiple measures of oxidative protection were found between H and L mice in liver (except for Glutathione Peroxidase), brain or mammary glands. Also, there were no associations between an individual’s energetic investment (e.g., MEO) and most of the oxidative stress measures detected in various tissues. These data are inconsistent with the oxidative stress theory, but were more supportive of, but not completely consistent, with the ‘oxidative shielding’ hypothesis.
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Affiliation(s)
- Aqeel H Al Jothery
- Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK.,Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Karbala, Karbala, Iraq
| | - Lobke M Vaanholt
- Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK
| | - Nimesh Mody
- Institute of Medical Sciences, University of Aberdeen, College of Life Sciences and Medicine, Foresterhill Health Campus, Aberdeen, United Kingdom
| | - Anis Arnous
- Section of Experimental Animal Models, Faculty of Health &Medical Sciences,University of Copenhagen, Denmark
| | - Jens Lykkesfeldt
- Section of Experimental Animal Models, Faculty of Health &Medical Sciences,University of Copenhagen, Denmark
| | - Lutz Bünger
- Animal and Veterinary Science Group, Scotland's Rural College (SRUC), Edinburgh EH9 3JG, UK
| | - William G Hill
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, UK
| | - Sharon E Mitchell
- Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK
| | - David B Allison
- School of Public Health, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - John R Speakman
- Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK.,Institute of Genetics and Developmental Biology, State Key Laboratory of Molecular Developmental Biology, Chinese Academy of Sciences, Beijing, People's Republic of China
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Rezende EL, Bacigalupe LD. Thermoregulation in endotherms: physiological principles and ecological consequences. J Comp Physiol B 2015; 185:709-27. [PMID: 26025431 DOI: 10.1007/s00360-015-0909-5] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 04/18/2015] [Accepted: 04/27/2015] [Indexed: 01/01/2023]
Abstract
In a seminal study published nearly 70 years ago, Scholander et al. (Biol Bull 99:259-271, 1950) employed Newton's law of cooling to describe how metabolic rates (MR) in birds and mammals vary predictably with ambient temperature (T a). Here, we explore the theoretical consequences of Newton's law of cooling and show that a thermoregulatory polygon provides an intuitively simple and yet useful description of thermoregulatory responses in endothermic organisms. This polygon encapsulates the region in which heat production and dissipation are in equilibrium and, therefore, the range of conditions in which thermoregulation is possible. Whereas the typical U-shaped curve describes the relationship between T a and MR at rest, thermoregulatory polygons expand this framework to incorporate the impact of activity, other behaviors and environmental conditions on thermoregulation and energy balance. We discuss how this framework can be employed to study the limits to effective thermoregulation and their ecological repercussions, allometric effects and residual variation in MR and thermal insulation, and how thermoregulatory requirements might constrain locomotor or reproductive performance (as proposed, for instance, by the heat dissipation limit theory). In many systems the limited empirical knowledge on how organismal traits may respond to environmental changes prevents physiological ecology from becoming a fully developed predictive science. In endotherms, however, we contend that the lack of theoretical developments that translate current physiological understanding into formal mechanistic models remains the main impediment to study the ecological and evolutionary repercussions of thermoregulation. In spite of the inherent limitations of Newton's law of cooling as an oversimplified description of the mechanics of heat transfer, we argue that understanding how systems that obey this approximation work can be enlightening on conceptual grounds and relevant as an analytical and predictive tool to study ecological phenomena. As such, the proposed approach may constitute a powerful tool to study the impact of thermoregulatory constraints on variables related to fitness, such as survival and reproductive output, and help elucidating how species will be affected by ongoing climate change.
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Affiliation(s)
- Enrico L Rezende
- Department of Life Sciences, University of Roehampton, Holybourne Avenue, London, SW15 4JD, UK.
| | - Leonardo D Bacigalupe
- Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, Valdivia, Chile.
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