Thermoregulation and survival during sepsis: insights from the cecal ligation and puncture experimental model

Abstract

Background: Sepsis remains a major global health concern due to its high prevalence and mortality. Changes in body temperature (Tb), such as hypothermia or fever, are diagnostic indicators and play a crucial role in the pathophysiology of sepsis. This study aims to characterize the thermoregulatory mechanisms during sepsis using the cecal ligation and puncture (CLP) model and explore how sepsis severity and ambient temperature (Ta) influence Tb regulation and mortality. Rats were subjected to mild or severe sepsis by CLP while housed at thermoneutral (28 °C) or subthermoneutral (22 °C) Ta, and their Tb was monitored for 12 h. Blood and hypothalamus were collected for cytokines and prostaglandin E₂ (PGE₂) analysis.

Results: At 28 °C, febrile response magnitude correlated with sepsis severity and inflammatory response, with tail vasoconstriction as the primary heat retention mechanism. At 22 °C, Tb was maintained during mild sepsis but dropped during severe sepsis, linked to reduced UCP1 expression in brown adipose tissue and less effective vasoconstriction. Despite differences in thermoregulatory responses, both Ta conditions induced a persistent inflammatory response and increased hypothalamic PGE₂ production. Notably, mortality in severe sepsis was significantly higher at 28 °C (80%) compared to 22 °C (0%).

Conclusions: Our findings reveal that ambient temperature and the inflammatory burden critically influence thermoregulation and survival during early sepsis. These results emphasize the importance of considering environmental factors in preclinical sepsis studies. Although rodents in experimental settings are often adapted to cold environments, these conditions may not fully translate to human sepsis, where cold adaptation is rare. Thus, researchers should carefully consider these variables when designing experiments and interpreting translational implications.

Keywords: Cytokines; Fever; Hypothalamus; Hypothermia; Mortality; PGE2.

Graphical representation of the thermoregulatory and inflammatory responses to mild and severe sepsis in rats housed at thermoneutral (28 °C) and subthermoneutral (22 °C) ambient temperatures (Ta). The model highlights distinct body temperature outcomes: fever and hypothermia. At thermoneutral Ta, severe sepsis induces a high fever, associated with increased hypothalamic PGE2, cytokine levels, and mortality, while mild sepsis leads to a moderate fever. In contrast, at subthermoneutral Ta, severe sepsis results in hypothermia with decreased UCP1 expression and lower mortality, whereas mild sepsis maintains normal body temperature. The impact of Ta on sepsis severity, thermoregulatory mechanisms, and survival is emphasized.

Fig. 1

Thermoregulatory responses of septic rats in a thermoneutral ambient temperature (28℃). Body temperature of sham and septic animals subjected to cecal ligation with 4 (CLP 4p—mild sepsis), 7 or 10 punctures (CLP 7p and CLP 10p, respectively—severe sepsis) (sham n = 8; CLP 4p n = 8; CLP 7p n = 7; CLP 10p n = 4) (a). Thermal index (area under the curve x time) of control and septic rats 2–5 h and 5–8 h after surgery (b). UCP1 expression in the BAT 12 h after sham or CLP surgery, values are represented as percentage of the control group (c). Heat loss index (HLI) variation (sham n = 8; CLP 4p n = 6; CLP 7p n = 7; CLP 10p n = 4) (d) and representative thermographic images (e) obtained 8 h after sepsis, the white arrows point to the Tsk measurement point. *p < 0.05 using one-way ANOVA with Tukey’s or Kruskal–Wallis post hoc test # p < 0.05 compared to sham group $ p < 0.05 comparing sham vs. CLP 7p and CLP 10p @ p < 0.05 comparing sham vs. CLP 4p groups. Data are presented as mean ± SD. n = 4–8

Fig. 2

Thermoregulatory responses of septic rats in a subthermoneutral ambient temperature (22℃). Body temperature of sham and septic animals subjected to cecal ligation with 4 (CLP 4p—mild sepsis) or 10 punctures (CLP 10p—severe sepsis) (sham n = 4; CLP 4p n = 6; CLP 10p n = 4) (a). Thermal index (area under the curve x time) of control and septic rats 2–5 h and 5–8 h after surgery (b). UCP1 expression in the BAT 12 h after sham or CLP surgery, values are represented as percentage of the control group (c). Heat loss index (HLI) variation (sham n = 4; CLP 4p n = 6; CLP 10p n = 4) (d) and representative thermographic images (e) obtained 10 h after sepsis, the white arrows point to the Tsk measurement point. *p < 0.05 using one-way ANOVA with Tukey’s or Kruskal–Wallis post hoc test # p < 0.05 compared to sham group @ p < 0.05 comparing sham vs. CLP 4p groups. Data are presented as mean ± SD. n = 4–8

Fig. 3

Survival rate 12 hours after sepsis in different ambient temperatures. Survival curve of animals subjected to mild (CLP 4p) and severe (CLP 7p and CLP 10p) sepsis in a thermoneutral (sham n = 8; CLP 4p n = 8; CLP 7p n = 8; CLP 10p n = 7) (a) and subthermoneutral (sham n = 4; CLP 4p n = 6; CLP 10p n = 5) (b) ambient temperature. c Values of the maximum body temperature of survivors (surv) versus non-survivor (non-surv) septic rats housed at 28℃ *p < 0.05 using a non-paired t-test. Data are presented as mean ± SD. n = 8–10

Fig. 4

PGE2 synthesis in the hypothalamus. Hypothalamic concentration (pg/mg protein) of PGE2 of septic and control animals in a thermoneutral (a) or subthermoneutral (b) ambient temperature. Samples were collected 12 hours after CLP/ sham surgeries. Data are presented as mean ± SD. *p < 0.05 using one-way ANOVA. n = 4–6

Fig. 5

Plasma inflammatory mediators during sepsis. Circulating levels of IL-6, IL-10 and IL-1β in septic and control rats in a thermoneutral (a) or subthermoneutral (b) ambient temperature. nd = nondetectable. Data are presented as mean ± SD. *p < 0.05 using a non-paired t-test. n = 4–7