Animals

Male mice (ICR strain, 5 weeks old, Sankyo Lab Service Co., Japan) were maintained until 6 weeks of age in a specific pathogen-free room with free access to water and food until the experiment was conducted.

Measurement of mouse rectal body temperature

After the rectal body temperature was confirmed to be at 37 °C or higher, 20% dried yeast saline suspension (Tanabe Mitsubishi Pharma Corporation, Tokyo, Japan) at 50 mL/kg was administered subcutaneously in the dorsal neck. Rectal body temperature was measured again 18 h after administration of the dried yeast solution, and mice with a fever of 0.8 °C or higher compared to their temperature before dried yeast solution administration were considered to be non-bacterial fever model mice. CPFX (LKT Laboratory, St. Paul, MN, USA), GFLX (LKT Laboratory), and LVFX (Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan) were intraperitoneally administered to yeast-induced fever model mice. The dose of CPFX and GFLX was adjusted to 100, 50, and 25 mg/kg (5 mL/kg) in saline solution. The dose of LVFX was adjusted to 100 and 50 mg/kg (5 mL/kg) in saline solution. The rectal body temperature was measured using a modified version of the method described by Ono et al. [10]. Briefly, each mouse was placed loosely in a small cloth bag, and a thermometer (MT-132, Mother Tool, Ueda, Japan) was inserted 25 mm into the rectum to measure body temperature every 6 min for 180 min after the administration of each FQ antimicrobial. Mice in the control group were intraperitoneally administered saline, and rectal body temperature was measured in the same manner. To avoid the anesthetic influence on body temperature, these manipulations were performed under unanesthetized conditions.

Evaluation of plasma concentrations of FQ antimicrobials in yeast-induced fever model mice

CPFX (100 mg/kg, 5 mL/kg), GFLX (100 mg/kg, 5 mL/kg), and LVFX (100 mg/kg, 5 mL/kg) were administered intraperitoneally to yeast-induced fever model mice. At 10, 20, 30, 45, 60, 90, 120, and 180 min after administration, mice were euthanized, and blood samples were collected. Blood samples were immediately centrifuged (4 °C, 3000 rpm, 10 min), and the resulting plasma FQ antimicrobial concentration was determined using high-performance liquid chromatography. The equipment and measurement conditions used were as follows: Pump, L-7100 (Hitachi, Ltd.); column oven unit, L-7300 (manufactured by Hitachi, Ltd.); sample injector, MICROLITER #705 (Kyowa Seimitsu Co., Ltd.); autosampler, L-2200 (Hitachi, Ltd.); pre-column, TSKguardgel ODS-80TM (7 mm, Tosoh Corp.); column, TSK-GEL ODS-80TM (250 mm × 4.6 mm i.d., 7 mm, Tosoh); fluorescence detector, L-7485 (Hitachi, Ltd.); column temperature, 23 °C; flow rate, 1 mL/min; mobile phase A, 10 mM sodium dodecyl sulfate (Nacalai Tesque Co., Kyoto, Japan) + 10 mM tetrabutylammonium acetate (Sigma Chemical Co., St. Louis, MO, USA) + 25 mM citric acid (Nacalai Tesque Co., Kyoto, Japan); mobile phase B, acetonitrile (Nacalai Tesque Co., Kyoto, Japan) (A:B = 57:43, v/v); wavelength (excitation/fluorescence), 280 nm/450 nm.

Rectal body temperature in yeast-induced fever model mice during preadministration of aminoglutethimide (AMG)

AMG (Sigma Chemical Co., St. Louis, MO, USA, 25 mg/kg, 5 mL/kg) solution was administered intraperitoneally to yeast-induced fever model mice. Sixty minutes later, GFLX (100 mg/kg, 5 mL/kg) was administered intraperitoneally, and the rectal body temperature was measured every 6 min until 180 min after GFLX administration.

Statistical analysis

All data are expressed as mean ± S.E. Dunnett's test was employed to analyse the significance of changes in rectal body temperature over time after intraperitoneal administration of FQ antimicrobials. Regarding the significance analysis, one-way ANOVA with the Bonferroni test was used to examine changes in rectal body temperature following glucocorticoid production inhibitor. A two-tailed difference was considered significant (P < 0.05). SPSS version 29.0 for Windows (IBM Corp., Armonk, NY, USA) was used for statistical analyses.