Saline as a vehicle control does not alter ventilation in male CD-1 mice

Abstract

Saline (0.9% NaCl) is used in clinical and research settings as a vehicle for intravenous drug administration. While saline is a standard control in mouse studies, there are reports of hyperchloremic metabolic acidosis in high doses. It remains unknown if metabolic acidosis occurs in mice and/or if compensatory increases in breathing frequency and tidal volume accompany saline administration. It was hypothesized that saline administration alters blood pH and the pattern of breathing in conscious CD‐1 male mice exposed to air or hypoxia (10% O2, balanced N2). Unrestrained barometric plethysmography was used to quantify breathing frequency (breaths/min; bpm), tidal volume (VT; mL/breath/10 g body weight (BW)), and minute ventilation (VE; mL/min/10 g BW) in two designs: (1) 11‐week‐old mice with no saline exposure (n = 11) compared to mice with 7 days of 0.9% saline administration (intraperitoneal, i.p.; 10 mL/kg body mass; n = 6). and (2) 17‐week‐old mice tested before (PRE) and after 1 day (POST1, n = 6) or 7 days (POST7, n = 5) of saline (i.p.; 10 mL/kg body mass). There were no differences when comparing frequency, VT, or VE between groups for either design with room air or hypoxia exposures. Hypoxia increased frequency, VT, and VE compared to room air. Moreover, conscious blood sampling showed no differences in pH, pa CO 2, paO2, or HCO3− in mice without or with 7 days of saline. These findings reveal no differences in ventilation following 1 and/or 7 days of saline administration in mice. Therefore, the use of 0.9% saline as a control is supported for studies evaluating the control of breathing in mice.

Young and middle‐aged mouse breathing behavior during the light and dark cycles

“…; Receno et al. ,b) for air breathing, this time span of calm breathing was not observed in these groups of mice, even after multiple chamber habituation days and over 3 h in the chamber during testing. Based on this behavior, we aimed to find a more appropriate way to quantify air breathing that could be used to compare mice in various conditions (e.g., young, old, light, dark).…”

“…; Receno et al. ). VT and/or VE are also altered by factors such as humidity, barometric pressure and temperature (Mortola and Frappell ), which can differ between laboratory setups, and could change on a day to day basis, although the Drorbaugh and Fenn equation does take into account the influence of these parameters.…”

“…; Receno et al. ,b). Alternative experimental designs have used baselines where measures are analyzed after a predetermined length of time (DeRuisseau et al.…”

“…Whole body unrestrained barometric plethysmography was utilized as previously described (Receno et al. ,b); mice were tested during hours 4–7 of the light cycle and 4–7 of the dark cycle. Briefly, mice were moved to the testing room shortly after calibration of the unrestrained barometric plethysmography set up.…”

“…; Receno et al. ,b). In this case, the calm breathing segment used to evaluate the response to gas exposures (hypoxia, hypercapnia, hypoxic hypercapnia) is intended to result in a point by point comparison without the confounds of additional chamber activity.…”