Physiological glomerular filtration rate and responses to Zeitgeber time and cold stress in C57BL/6 mice

Transcutaneous FITC-sinistrin clearance provides a minimally invasive method to measure real-time glomerular filtration rate (GFR) in small animals. However, large-scale physiological reference data and analyses of time-of-day and environmental temperature influences remain limited. We aimed to establish reference values for GFR in healthy C57BL/6 mice and to assess variations related to Zeitgeber timing and cold stress. A total of 200 male mice were studied using a transcutaneous GFR monitoring system under standard conditions, at four Zeitgeber points (ZT2, ZT8, ZT14, ZT18), and following exposure to 4 °C for 2 or 4 h. Baseline GFR was 1.215 ± 0.201 mL/min/100 g body weight. Four-hour cold exposure increased GFR (1.129 ± 0.207 to 1.541 ± 0.333, p = 0.0004), while 2-hour exposure showed a non-significant trend (p = 0.0795). No significant differences were observed among Zeitgeber timepoints (p = 0.5317), though slightly elevated levels were noted during the active (dark) phase. This study provides baseline GFR reference values for healthy C57BL/6 mice and indicates that GFR is responsive to cold stress but remains relatively stable across the light-dark cycle, offering essential data for future renal physiology and experimental nephrology research.