Gender Comparisons of Control of Breathing and Metabolism in Conscious Mice Exposed to Cold

Abstract

We evaluated the effects of 2 h of warm (24°C) and cold (6°C) exposure on metabolism and ventilation (v̇_E) in conscious male and female Harlan ICR Swiss Webster mice exposed to air, and 8% O₂ in N₂ (hypoxia) and to 5% CO₂ in O₂ (hypercapnia) for 2 min each at both temperatures. All cold-exposed mice increased O₂ consumption (v̇_O2), and maintained body temperature. Cold-exposed females doubled their tidal volume, increased their v̇_E fivefold, and doubled their ventilatory equivalent to v̇_O2 (v̇_E/v̇_O2). In contrast, cold-exposed males decreased tidal volume and doubled v̇_E relative to warm exposure. The ventilatory equivalent of males was similar during warm and cold exposure. During warm exposure, mice of both genders increased their ventilatory responses to both hypoxia and to hypercapnia by different mechanisms. In contrast, during cold exposure, these responses were blunted relative to air measurements in females and decreased below air values in males. Thus, cold exposure was able to elicit gender-specific ventilatory and metabolic responses.