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The prolactin responses to active and passive heating in man
David Low1, Alison Purvis, Thomas Reilly
1Research Institute for Exercise and Environmental Medicine, Liverpool John Moores University, Liverpool L3 2ET, UK. davidlow@texashealth.org
Experimental Physiology
|September 15, 2005
Summary
This study found that core body temperature, not blood pressure, drives prolactin release during heat stress. This suggests thermoregulation, not cardiovascular strain, signals central fatigue during exercise in the heat.
Area of Science:
- Exercise Physiology
- Thermoregulation
- Endocrinology
Background:
- Prolactin is an indirect marker of central fatigue.
- Understanding factors influencing prolactin release during heat stress is crucial for exercise performance and safety.
Purpose of the Study:
- To compare prolactin and blood pressure responses to active (exercise) and passive (water bath) heat stress at identical core temperatures.
- To determine if thermoregulatory or cardiovascular factors are the primary stimulus for prolactin release during heat exposure.
Main Methods:
- Twelve male subjects underwent two trials: cycling to exhaustion in a 33°C room (active) and passive heating in a 41.56°C water bath.
- Blood samples were collected to measure serum prolactin levels.
- Core body temperature and mean arterial blood pressure were monitored throughout both trials.
Main Results:
- Core body temperature was similar between active and passive heating (approximately 38.8°C).
- Mean arterial blood pressure was significantly lower during passive heating compared to active heating.
- Serum prolactin levels did not differ significantly between active and passive heating, despite blood pressure variations.
Conclusions:
- Thermoregulatory signals, specifically core body temperature, appear to be the primary stimulus for prolactin release during heat stress.
- Cardiovascular afferents do not seem to be the key driver of prolactin release in this context.
- These findings suggest that core temperature is a more critical factor than cardiovascular strain in signaling central fatigue during exercise in the heat.