EFFECT OF GENDER ON THERMOREGULATION AND SURVIVAL OF HYPOXIC RATS

1. Hypothermia is a documented response to hypoxia but little is known about possible gender differences, Because female rats have a greater hypoxic ventilatory response than males, we hypothesized that females would be more tolerant of hypoxia, We studied 18 female and 18 male L ong-Evans rats, 2. Radiotelemetry transmitters for body temperature (T b) were implanted under general anaesthesia (90 mg/mL ketamine and 10 mg/mL xylazine; 0.1 mL/100 g bodyweight, i.p.), 3. Rats were exposed t o 21, 16, 12, 10, 8, 6, 4 and 2% O-2 (balance N-2) for 30 min each in chambers kept at either 31 degrees C (clamped) or 20 degrees C (hypoth ermic), Survival was defined as ataxic and unresponsive. 4, Females we re more hypoxia tolerant than males, often enduring 2% inspired O-2 (1 3 km altitude), 5. This was correlated with a lower Tb in the hypother mic group, but not in the clamped group, 6, Hypothermia increased 'sur vival' of rats independent of gender, 7. When Tb was clamped, female r ats showed significantly greater survival than males, 8. Thus, separat e mechanisms (hypothermia or ventilation) may be acting to increase to lerance of clamped and hypothermic female rats to severe hypoxia.