Skip to main content

A mouse is not a rat is not a man: species-specific metabolic responses to sepsis - a nail in the coffin of murine models for critical care research?

“All models are wrong, but some are useful.”

-Box GEP, Draper NR (1987) Empirical model-building and response surface, Wiley

Sepsis and consequent multi-organ failure are the leading causes of mortality in critically ill patients. Numerous therapeutic strategies, which yielded promising results in preclinical studies, have failed to show any efficacy in clinical trials. Historically, most of our (patho)physiological understanding of cardiovascular regulation in health and disease has been established in larger mammals, e.g., dog, pig, and sheep. However, a very large body of the literature collected over recent decades originates from investigations in rodents. Despite their small size, which makes surgery difficult and limits repetitive blood sampling, murine models have been widely used, not because they are more faithful to adult human pathophysiology than larger mammals but because they are inexpensive, easy to handle and care for, and with availability of gene knockout and overexpression strains. Investigators have performed studies without necessarily having a good appreciation of some fundamental differences in the physiology of rodents. These have been long established by comparative physiologists, yet have never been taught in any medical school. One can query the logic of inferring information on mechanisms involved in septic shock using species capable of decreasing their high resting metabolic rate both rapidly and massively, and with the associated circulatory and respiratory responses.

Mouse models of acute inflammatory disorders have recently been questioned by Seok et al. [1] who found that “genomic responses to different acute inflammatory stresses are highly similar in humans”, whereas “these responses are not reproduced in current mouse models”. In this context, Zolfaghari et al. [2] compared the metabolic responses to polymicrobial sepsis in rats and mice. Their main findings were that mice presented with a progressive drop in whole body O2 uptake and a concurrent fall in body temperature, which was only partially restored by external warming. This marked metabolic depression coincided with pronounced impairment of left heart systolic contractility. In sharp contrast, only severely ill rats showed a comparably decreased cardiac output, and the metabolic depression was only present during the late premortem period.

How can we explain these findings by Zolfaghari et al. [2]? The authors have the merit of raising an issue of crucial importance for critical care research, i.e., whether or not murine models can yield sufficient information to enable a good design of clinical studies. In particular, they must be commended for having achieved not only an identical 72-h mortality but also comparable 24-h clinical severity scores. This is by no means trivial in the two species investigated: body weight differs by an order of magnitude, and mice present with a twofold to threefold higher metabolic expenditure on a per gram basis. Interestingly, albeit the final outcome was identical, the time course of the clinical development of sepsis differed: the clinical severity score was already higher in mice with “severe” sepsis at 6 h post inoculation of feces, whereas in rats, this difference was only apparent at 24 h. One might argue that the resuscitation technique may have assumed importance in this context: rats were infused with continuous i.v. fluids via a jugular venous catheter inserted prior to the experiment, while mice received intermittent s.c. bolus administration. Moreover, even sham-operated mice showed moderate hyperlactatemia, hyperglycemia, and hyperchloremia, and, in particular, marked metabolic acidosis. The latter is a common finding in mouse models reported by other authors [3, 4], even when balanced electrolyte solutions rather than saline were used as maintenance fluids [5, 6]. This prompted some authors to systemically administer bicarbonate infusions [7].

The authors' observation of markedly reduced energy expenditure and consecutive hypothermia in mice is not new and is most likely due to the fundamentally different metabolic response in this species rather than to any of the abovementioned phenomena: in response to tissue hypoxia, mice reduce their energy expenditure by decreasing “nonshivering thermogenesis”. Nonshivering thermogenesis [8] as a result of the high activity of mitochondrial uncoupling proteins [9] represents a very large proportion of overall O2 consumption which can therefore be depressed very rapidly without affecting ATP production. Such a regulation of metabolism represents a unique protective adaptation, observable in many species including human babies. Reduced VO2 can be observed during hemorrhagic shock or severe hypoxia in rats [10], but this response is less pronounced in adult individuals [11, 12]. In other words, even “small animal model species are not created equal” [13]. Hence, whenever interventions target or affect cellular energy metabolism [14, 15], results obtained in mouse models may be misleading. In keeping with their thermal and metabolic regulation, the physiology of an adult mouse is much closer to that of a premature newborn baby than an adult rat!

Consequently, should we abandon mouse models for critical care research and replace them with rats? Undoubtedly, rats are easier to handle than mice, and they have a 10 to 20 times higher blood volume. However, in rats, the response to injury may also markedly differ from that of humans, in particular with respect to mediators that are referred to assume crucial importance during sepsis. For example, rats present with blood concentrations of nitric oxide (NO) metabolites that are 10 to 20 times higher than those in humans. Moreover, they are particularly resistant to oxidative stress, a common phenomenon during sepsis, due to their high tissue activity of antioxidant enzymes [16, 17]. Indeed, there is an abundant literature on promising rat studies of antioxidants or NO inhibitors, which have never translated into clinical practice. However, this problem is inherent to the use of other “nonhuman” models; mice, for instance, also show different activity for inducible NO synthase (iNOS)-related NO release [18, 19]. As a consequence, one might consider only using large animal species, e.g., swine, dogs, or ewes. However, in addition to cost, labor, and specific ethical concerns of the lay public, there is no ideal large animal species either which fits all needs: The use of ruminants may be questioned when gastrointestinal function is to be investigated due to their different anatomy. Despite their general similarity with humans, swine can be a problem when they are used in targeting lung mechanics and perfusion due to a lack of collateral alveolar ventilation and a marked pulmonary hypertensive response.

Finally, due to their experimental design covering several days, Zolfaghari et al. [2] could not address the question whether it is necessary - and if so, to what extent - to integrate standard intensive care procedures into an experimental design, ultimately to guarantee clinical relevance for critical care research. The rationale for this discussion is self-evident and was highlighted by the late Prof. Daniel Traber more than a decade ago, “Would you…accept data on a septic patient who was not resuscitated…, …who did not even have blood pressures and heart rates monitored?” [20]. This point is essential since although murine models are very different from humans due to their own evolutionary specificities, when it comes to shock or its treatment, the persistence of fundamental responses shared by all mammals must be acknowledged. For instance, striking similarities exist between all species as well as through the different ages (from premature babies to elderly patients) as far as the principles of treatment of septic shock (antibiotics, volume replacement, etc.…) are concerned. Although the time course of the clinical development of sepsis differed between rats and mice, in the study of Zolfaghari et al. [2], the final outcome was identical in both species. Whenever standard ICU strategies are used [21, 22], the similarities between models become even more obvious, regardless of differences in physiological regulation, level of inflammation, temperature, and VO2 or NO regulation. For instance, as demonstrated by Hollenberg [22], the mortality of mice 48 h after cecal ligation and puncture was close to 100% without resuscitation, whereas fluids and antibiotic therapy resulted in 45% survival, a value close to the clinical setting. For obvious technical reasons, the smaller the species studied, the more challenging the intensive care-type measurements during an experiment are. Consequently, this problem is much more pronounced in murine than in rat models. The use (or lack) of mechanical ventilation or hemodynamic monitoring is a prominent example. The miniaturization of equipment will certainly allow many limitations to be overcome, but will of course not solve fundamental species-specific differences. Although it would be interesting to develop methods to reduce basal metabolic rate in humans based on the response seen a mouse model, relevant qualitative as well as semiquantitative information on the benefits of therapeutic strategies could still be obtained using small mammals. Similar to the vast majority of researchers, Zolfaghari et al. [2] used young, male, and otherwise healthy animals. These certainly do not represent the majority of ICU patients who are often elderly with chronic preexisting comorbidities. Age, gender, and comorbidities influence outcomes not only in patients but also in experimental models of sepsis [2332].

Hence, as a bottom line conclusion, Zolfaghari et al. [2] highlighted an important issue of translational research in critical care medicine, i.e., that data on the physiological response to septic shock in a mouse or a rat model can only be understood in keeping with the frame of reference of the animal’s physiology. Such data cannot be directly extrapolated to septic patients. The hope is that by acknowledging and understanding these differences, the resources involved with murine models will not be wasted and that rodents could be continued to be used, with a rational frame of reference based on objective elements of comparative pathophysiology - rather than physiology - a discipline which is still in its very early age and which remains to be developed. Only then could mouse models take their real place in critical care research along with large animal investigations and in vitro (i.e., reductionist) approaches before commencement of any clinical trial.


  1. 1.

    Seok J, Warren HS, Cuenca AG, Mindrinos MN, Baker HV, Xu W, Richards DR, McDonald-Smith GP, Gao H, Hennessy L, Finnerty CC, López CM, Honari S, Moore EE, Minei JP, Cuschieri J, Bankey PE, Johnson JL, Sperry J, Nathens AB, Billiar TR, West MA, Jeschke MG, Klein MB, Gamelli RL, Gibran NS, Brownstein BH, Miller-Graziano C, Calvano SE, Mason PH, et al.: Genomic responses in mouse models poorly mimic human inflammatory diseases. Proc Natl Acad Sci USA 2013, 110: 3507–3512. 10.1073/pnas.1222878110

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  2. 2.

    Zolfaghari PS, Pinto BB, Dyson A, Singer M: The metabolic phenotype of rodent sepsis: cause for concern? Intensive Care Med Exp 2013. in press

    Google Scholar 

  3. 3.

    Volpato GP, Searles R, Yu B, Scherrer-Crosbie M, Bloch KD, Ichinose F, Zapol WM: Inhaled hydrogen sulfide: a rapidly reversible inhibitor of cardiac and metabolic function in the mouse. Anesthesiology 2008, 108: 659–668. 10.1097/ALN.0b013e318167af0d

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  4. 4.

    Reiss LK, Kowallik A, Uhlig S: Recurrent recruitment manoeuvres improve lung mechanics and minimize lung injury during mechanical ventilation of healthy mice. PLoS One 2011, 6: e24527. 10.1371/journal.pone.0024527

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  5. 5.

    Wagner F, Scheuerle A, Weber S, Stahl B, McCook O, Knöferl MW, Huber-Lang M, Seitz DH, Thomas J, Asfar P, Szabó C, Möller P, Gebhard F, Georgieff M, Calzia E, Radermacher P, Wagner K: Cardiopulmonary, histologic, and inflammatory effects of intravenous Na 2 S after blunt chest trauma-induced lung contusion in mice. J Trauma 2011, 71: 1659–1667. 10.1097/TA.0b013e318228842e

    CAS  PubMed  Article  Google Scholar 

  6. 6.

    Wagner F, Wagner K, Weber S, Stahl B, Knöferl MW, Huber-Lang M, Seitz DH, Asfar P, Calzia E, Senftleben U, Gebhard F, Georgieff M, Radermacher P, Hysa V: Inflammatory effects of hypothermia and inhaled H 2 S during resuscitated, hyperdynamic murine septic shock. Shock 2011, 35: 396–402. 10.1097/SHK.0b013e3181ffff0e

    CAS  PubMed  Article  Google Scholar 

  7. 7.

    Wolthuis EK, Vlaar AP, Choi G, Roelofs JJ, Juffermans NP, Schultz MJ: Mechanical ventilation using non-injurious ventilation settings causes lung injury in the absence of pre-existing lung injury in healthy mice. Crit Care 2009, 13: R1. 10.1186/cc7688

    PubMed Central  PubMed  Article  Google Scholar 

  8. 8.

    Mortola JP: Hypoxic hypometabolism in mammals. News Physiol Sci 1993, 8: 79–82.

    Google Scholar 

  9. 9.

    van Marken Lichtenbelt WD, Schrauwen P: Implications of non-shivering thermogenesis for energy balance regulation in humans. Am J Physiol Regul Integr Comp Physiol 2011, 301: R285-R296. 10.1152/ajpregu.00652.2010

    CAS  PubMed  Article  Google Scholar 

  10. 10.

    Haouzi P, Van de Louw A: Uncoupling mitochondrial activity maintains body VO 2 during hemorrhage-induced O 2 deficit in the anesthetized rat. Respir Physiol Neurobiol 2013, 186: 87–94. 10.1016/j.resp.2012.12.006

    CAS  PubMed  Article  Google Scholar 

  11. 11.

    Frappell P, Lanthier C, Baudinette RV, Mortola JP: Metabolism and ventilation in acute hypoxia: a comparative analysis in small mammalian species. Am J Physiol 1992, 262: R1040-R1046.

    CAS  PubMed  Google Scholar 

  12. 12.

    Haouzi P, Bell HJ, Notet V, Bihain B: Comparison of the metabolic and ventilatory response to hypoxia and H 2 S in unsedated mice and rats. Respir Physiol Neurobiol 2009, 167: 316–322. 10.1016/j.resp.2009.06.006

    CAS  PubMed  Article  Google Scholar 

  13. 13.

    Dobson GP: Small animal model species are not created equal. Crit Care Med 2012, 40: 711.

    PubMed  Article  Google Scholar 

  14. 14.

    Haouzi P: Murine models in critical care research. Crit Care Med 2011, 39: 2290–2293. 10.1097/CCM.0b013e3182227550

    PubMed  Article  Google Scholar 

  15. 15.

    Wagner K, Calzia E, Georgieff M, Radermacher P, Wagner F: A mouse is not a man: should we abandon murine models in critical care research? Crit Care Med 2011, 39: 2371–2373. 10.1097/CCM.0b013e318224995d

    PubMed  Article  Google Scholar 

  16. 16.

    Godin DV, Garnett ME: Species-related variations in tissue antioxidant status—I. Differences in antioxidant enzyme profiles. Comp Biochem Physiol B 1992, 103: 737–742.

    CAS  PubMed  Google Scholar 

  17. 17.

    Godin DV, Garnett ME: Species-related variations in tissue antioxidant status—II. Differences in susceptibility to oxidative challenge. Comp Biochem Physiol B 1992, 103: 743–748.

    CAS  PubMed  Google Scholar 

  18. 18.

    Reade MC, Young JD: Of mice and men (and rats): implications of species and stimulus differences for the interpretation of studies of nitric oxide in sepsis. Br J Anaesth 2003, 90: 115–118. 10.1093/bja/aeg033

    CAS  PubMed  Article  Google Scholar 

  19. 19.

    Bauer M, Reinhart K: From mice and MOF: rodent models, immune modulation, and outcome in the critically ill. Crit Care Med 2006, 43: 912–923.

    Google Scholar 

  20. 20.

    Traber DL: Expired nitric oxide and shock in high order species. Crit Care Med 1999, 27: 255–256. 10.1097/00003246-199902000-00021

    CAS  PubMed  Article  Google Scholar 

  21. 21.

    Fink MP, Heard SO: Laboratory models of sepsis and septic shock. J Surg Res 1990, 49: 186–196. 10.1016/0022-4804(90)90260-9

    CAS  PubMed  Article  Google Scholar 

  22. 22.

    Hollenberg SM: Mouse models of resuscitated shock. Shock 2005,24(Suppl 1):58–63.

    PubMed  Article  Google Scholar 

  23. 23.

    Khan AI, Coldewey SM, Patel NS, Rogazzo M, Collino M, Yaqoob MM, Radermacher P, Kapoor A, Thiemermann C: Erythropoietin attenuates cardiac dysfunction in experimental sepsis in mice via activation of the β-common receptor. Dis Model Mech 2013, 6: 1021–1030. 10.1242/dmm.011908

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  24. 24.

    Drechsler S, Weixelbaumer K, Raeven P, Jafarmadar M, Khadem A, van Griensven M, Bahrami S, Osuchowski MF: Relationship between age/gender-induced survival changes and the magnitude of inflammatory activation and organ dysfunction in post-traumatic sepsis. PLoS One 2012, 7: e51457. 10.1371/journal.pone.0051457

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  25. 25.

    Kaplan JM, Nowell M, Lahni P, O’Connor MP, Hake PW, Zingarelli B: Short-term high fat feeding increases organ injury and mortality after polymicrobial sepsis. Obesity 2012, 20: 1995–2002. 10.1038/oby.2012.40

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  26. 26.

    Osuchowski MF, Craciun FL, Schuller E, Sima C, Gyurko R, Remick DG: Untreated type 1 diabetes increases sepsis-induced mortality without inducing a prelethal cytokine response. Shock 2010, 34: 369–376. 10.1097/SHK.0b013e3181dc40a8

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  27. 27.

    Turnbull IR, Clark AT, Stromberg PE, Dixon DJ, Wollsey CA, Davis CG, Hotchkiss RS, Buchman TG, Coopersmith CM: Effects of aging on the immunopathologic response to sepsis. Crit Care Med 2009, 37: 1018–1023. 10.1097/CCM.0b013e3181968f3a

    CAS  PubMed Central  PubMed  Article  Google Scholar 

  28. 28.

    Singer G, Stokes KY, Terao S, Granger DN: Sepsis-induced intestinal microvascular and inflammatory responses in obese mice. Shock 2009, 31: 275–279. 10.1097/SHK.0b013e3181834ab3

    CAS  PubMed  Article  Google Scholar 

  29. 29.

    Strandberg L, Verdrengh M, Enge M, Andersson N, Amu S, Önnheim K, Benrick A, Brisslert M, Bylund J, Bokarewa M, Nilsson S, Jansson JO: Mice chronically fed high-fat diet have increased mortality and disturbed immune response in sepsis. PLoS One 2009, 4: e7605. 10.1371/journal.pone.0007605

    PubMed Central  PubMed  Article  Google Scholar 

  30. 30.

    Miyaji T, Hu X, Yuen PST, Muramatsu Y, Iyer S, Hewitt SM, Star RA: Ethyl pyruvate decreases sepsis-induced acute renal failure and multiple organ damage in aged mice. Kidney Int 2003, 64: 1620–1631. 10.1046/j.1523-1755.2003.00268.x

    CAS  PubMed  Article  Google Scholar 

  31. 31.

    Saito H, Sherwood ER, Varma TK, Evers BM: Effects of aging on mortality, hypothermia, and cytokine induction in mice with endotoxemia or sepsis. Mech Ageing Dev 2003, 124: 1047–1058. 10.1016/j.mad.2003.08.002

    CAS  PubMed  Article  Google Scholar 

  32. 32.

    Turnbull IR, Wlzorek JJ, Osborne D, Hotchkiss RS, Coopersmith CM, Buchman TG: Effects of age on mortality and antibiotic efficacy in cecal ligation and puncture. Shock 2003, 19: 310–313. 10.1097/00024382-200304000-00003

    PubMed  Article  Google Scholar 

Download references


This publication is supported by the Klinische Forschergruppe 200 (KFO 200) “Die Entzündungsantwort nach Muskulo-Skeletalem Trauma” (Deutsche Forschungsgemeinschaft Ra 396/9-2).

Author information



Corresponding author

Correspondence to Peter Radermacher.

Additional information

Competing interests

Both authors declare that they have no competing interests.

Authors’ contributions

PR and PH drafted the manuscript, read, and approved the final version.

Rights and permissions

Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Reprints and Permissions

About this article

Cite this article

Radermacher, P., Haouzi, P. A mouse is not a rat is not a man: species-specific metabolic responses to sepsis - a nail in the coffin of murine models for critical care research?. ICMx 1, 7 (2013).

Download citation


  • Nitric Oxide
  • Septic Shock
  • Polymicrobial Sepsis
  • Metabolic Depression
  • Clinical Severity Score