The normal acid-base status of mice

Area of Science:

• Physiology
• Comparative Physiology
• Animal Models

Background:

• Rodent models are crucial for physiological studies, including acid-base regulation.
• Limited data exists on normal acid-base parameters in conscious mice, hindering accurate interpretation of studies using genetically modified strains.
• Existing studies often report blood gas values from anesthetized animals, which may not reflect physiological conditions.

Purpose of the Study:

• To characterize in vitro carbon dioxide (CO₂) binding characteristics of mouse blood.
• To determine the normal arterial acid-base status in conscious BALB/c mice.
• To compare acid-base parameters between conscious and anesthetized mice.

Main Methods:

• In vitro CO₂ dissociation curves were generated using whole blood equilibrated in rotating tonometers.
• Arterial blood gas analysis was performed on conscious mice with indwelling carotid artery catheters.
• Acid-base status, PCO₂, bicarbonate, and lactate concentrations were measured in both conscious and isoflurane-anesthetized mice.

Main Results:

• In vitro analysis revealed typical mammalian pK' and non-bicarbonate buffer capacity.
• Conscious mice exhibited a normal mammalian arterial pH (7.391 ± 0.026) with lower PCO₂ (30.3 ± 2.1 mm Hg) compared to larger mammals.
• Anesthesia with isoflurane significantly lowered arterial pH (7.239 ± 0.021) and increased PCO₂ (41.9 ± 2.9 mm Hg).

Conclusions:

• Mice possess an arterial pH comparable to other mammals, but with characteristically lower arterial PCO₂.
• Anesthesia significantly alters acid-base parameters in mice, making data from anesthetized animals unreliable for normal physiological reference.
• Accurate assessment of acid-base regulation in mice necessitates sampling from conscious animals via indwelling catheters, not terminal cardiac puncture under anesthesia.