Abstract
A reversible state of narcosis having certain characteristics of both hibernation and anesthesia may be induced and maintained for many hours in the rat and dog by sudden exposure at 5°C. to concentrations of CO2 of 5 per cent or greater. In this state the rat has a body temperature of 16-20°C., a heart rate of 30-100 per minute, and a respiratory rate of 1-20 per minute. When the rat is respiring 11% CO2 at 5°C. the CO2 content of the blood may reach 110 volumes per cent and the plasma pH a level of 7.07. A similar state may be induced in the rabbit by 20% CO2 and cold but it is not reversible because of the fatal pulmonary edema.
Rats are rendered more susceptible to this state by fasting, prolonged (three weeks) exposure to 10% O2, or by administration of small doses of depressant drugs.
Repeated narcotization by this method at intervals of several days; acclimatization to cold or to CO2 for several days; or previous thyroid feeding; renders the rat partially or completely resistant to the narcosis induced by 11% CO2 at 5°C.
A state of depression somewhat similar to, but not identical with, that described above may be produced in rats by exposure to low oxygen tensions (10%) or to high oxygen tensions (4 atmospheres) at an environmental temperature of 5°C.
It is believed that these experiments furnish additional evidence to support the view that a sudden and well marked increase in the tissue tension of CO2 produces a definite, if temporary, decrease in the total oxidative metabolism and a parallel reduction in activity of certain body tissues including some portions of the nervous system.
Footnotes
- Received April 1, 1943.
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