Metabolic reduction in hypothermia: pathophysiological problems and natural examples--Part 2

Area of Science:

• Physiology
• Zoology
• Biophysics

Background:

• Hibernation in mammals is a key example of spontaneous cooling in homeotherms.
• Mammalian cold tolerance is hypothesized to be limited by a specific minimal metabolic rate.
• Acid-base balance may modulate metabolic rate during natural lethargic states.

Purpose of the Study:

• To investigate the common specific minimal metabolic rate limiting mammalian cold tolerance.
• To explore the influence of acid-base balance on metabolic rate during hypothermia.
• To assess the feasibility of profound hypothermia in large homeotherms.

Main Methods:

• Analysis of metabolic turnover rates at regulated minimal body temperatures in hibernating mammals.
• Examination of the relationship between metabolic rate and body temperature in natural lethargic states.
• Theoretical considerations on the temperature dependence of metabolic processes and acid-base balance.

Main Results:

• A uniform turnover rate related to body weight was observed in hibernators at minimal body temperatures.
• Larger mammals may reach the minimal metabolic rate limit at less profound hypothermia due to lower basal metabolism.
• Metabolic processes with differing temperature dependencies disintegrate upon cooling, more so in intermediate ranges.

Conclusions:

• Mammalian cold tolerance is generally limited by a common specific minimal metabolic rate.
• Acid-base balance likely plays a modulating role in metabolic rate during hypothermia.
• Short-duration, profound hypothermia may be achievable in large homeotherms under specific rewarming conditions.