Divergent physiological responses in laboratory rats and mice raised at high altitude
Fecha
2015-01-29Autor
Jochmans-Lemoine, Alejandra
Villalpando, Gabriela
Gonzales, Marcelino
Valverde, Ibana
Soria, Rudy
Joseph, Vincent
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Abstract.
Ecological studies show that mice can be found at high altitude (HA – up to 4000 m) while rats are absent at these altitudes, and there are
no data to explain this discrepancy. We used adult laboratory rats and
mice that have been raised for more than 30 generations in La Paz,
Bolivia (3600 m), and compared their hematocrit levels, right
ventricular hypertrophy (index of pulmonary hypertension) and
alveolar surface area in the lungs. We also used whole-body
plethysmography, indirect calorimetry and pulse oxymetry to
measure ventilation, metabolic rate (O2 consumption and CO2
production), heart rate and pulse oxymetry oxygen saturation (pO2,sat)
under ambient conditions, and in response to exposure to sea level
PO2 (32% O2=160 mmHg for 10 min) and hypoxia (18% and 15%
O2=90 and 75 mmHg for 10 min each). The variables used for
comparisons between species were corrected for body mass using
standard allometric equations, and are termed mass-corrected
variables. Under baseline, compared with rats, adult mice had
similar levels of pO2,sat, but lower hematocrit and hemoglobin levels,
reduced right ventricular hypertrophy and higher mass-corrected
alveolar surface area, tidal volume and metabolic rate. In response to
sea level PO2 and hypoxia, mice and rats had similar changes of
ventilation, but metabolic rate decreased much more in hypoxia in
mice, while pO2,sat remained higher in mice. We conclude that
laboratory mice and rats that have been raised at HA for >30
generations have different physiological responses to altitude. These
differences might explain the different altitude distribution observed in
wild rats and mice.