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Clonidine decreases vasoconstriction and shivering thresholds, without affecting the sweating threshold
G Nicolaou1, A A Chen, C E Johnston
1Laboratory for Exercise and Environmental Medicine, Health, Leisure and Human Performance Research Institute, Winnipeg, Manitoba, Canada.
Summary
Clonidine, a medication, lowers core body temperature thresholds for vasoconstriction and shivering in a dose-dependent manner. It does not affect the sweating threshold but widens the range between sweating and vasoconstriction.
Area of Science:
- Physiology
- Pharmacology
- Thermoregulation
Background:
- Clonidine is an alpha-adrenergic agonist with known effects on the central nervous system.
- Understanding its impact on human thermoregulation is crucial for clinical applications.
Purpose of the Study:
- To investigate the dose-dependent effects of clonidine on human thermoregulatory thresholds.
- To test if clonidine alters sweating, vasoconstriction, and shivering thresholds.
Main Methods:
- Six healthy subjects received oral clonidine doses (0, 3, 6, 9 µg/kg) in a double-blind, balanced design.
- Core and mean skin temperatures were measured while subjects were immersed in water.
- Thermoregulatory thresholds for sweating, vasoconstriction, and shivering were determined and adjusted to a mean skin temperature of 33°C.
Main Results:
- Clonidine significantly decreased core temperature thresholds for vasoconstriction (1.16°C) and shivering (1.63°C) at high doses.
- Dose-response effects were linear, with thresholds decreasing by 0.13°C and 0.19°C per µg/kg for vasoconstriction and shivering, respectively.
- The sweating threshold remained unchanged, but the interthreshold range between sweating and vasoconstriction increased significantly with clonidine.
Conclusions:
- Clonidine inhibits central thermoregulation, evidenced by lowered thresholds for cold responses.
- The observed effects are comparable to those of certain anesthetic agents and opioids.
- These findings highlight clonidine's potential to alter the body's core temperature regulation mechanisms.