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

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% O-2, balanced N-2). Unrestrained barometric plethysmography was used to quantify breathing frequency (breaths/min; bpm), tidal volume (VT; mL/breath/10g body weight (BW)), and minute ventilation (VE; mL/min/10g 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.; 10mL/kg body mass; n=6). and (2) 17-week-old mice tested before (PRE) and after 1 day (POST1, n=6) or 7days (POST7, n=5) of saline (i.p.; 10mL/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, p(aCO2), p(aO2), or HCO3- in mice without or with 7days of saline. These findings reveal no differences in ventilation following 1 and/or 7days 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.