The Effects of Hypobaric Pressure on Thermoregulation in The Unrestrained New Zealand White Rabbit, Oryctolagus Cuniculus
Weenig, Jay Frederick
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https://hdl.handle.net/2142/71418
Description
Title
The Effects of Hypobaric Pressure on Thermoregulation in The Unrestrained New Zealand White Rabbit, Oryctolagus Cuniculus
Author(s)
Weenig, Jay Frederick
Issue Date
1982
Department of Study
Physiology and Biophysics
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Abstract
The thermoregulatory responses of unrestrained New Zealand white rabbits were studied in relation to altitudes of 20,000 feet, 25,000 and 30,000 feet, and at ambient temperatures of 0(DEGREES)C, 15(DEGREES)C and 25(DEGREES)C at these three altitudes. Forty-two adult male New Zealand white rabbits were used in this research. The preoptic area of the brain was heated and cooled at these ambient temperatures while monitoring metabolism, ear pinna temperature, back temperature, preoptic temperature, breathing rate and heart rate.
The ear vessels of the rabbits opened abruptly when ascending to 24,000 feet of altitude at ambient temperature of either 0(DEGREES)C or 15(DEGREES)C. The abrupt opening of the ear vessels caused an immediate increase in ear temperature of more than 20(DEGREES)C.
Heating and cooling the preoptic at high altitude (less than 349 mm/Hg) showed different thermoregulatory responses in the rabbits than seen at ground level (above 650 mm/Hg). Cooling the preoptic at altitude (less than 349 mm/Hg) at 15(DEGREES)C and 25(DEGREES)C ambient temperature had little or no effect on ear pina temperature as compared to ground level (above 650 mm/Hg) which showed a marked decrease in ear pinna temperature.
Heart rate was greatly increased by the stresses of high altitude and hypoxia, especially when the preoptic was heated. The rabbits did not show a marked increase in metabolism as would be expected and, when exposed to these stresses, could not adequately respond to preoptic temperature changes.
The rabbits exhibited extreme hyperventilation when they were near the maximal stress point and the preoptic was heated. This event did not occur if they were at maximum stress (30,000 feet) when the preoptic was heated. On initial ascent to altitude the rabbits would use the ball posture (more compact, heat-conserving) regardless of ambient temperature.
In summary, when rabbits are stressed by high altitude they exhibit different thermoregulatory responses when the preoptic temperature is changed than they exhibit at ground level (above 650 mm/Hg).
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