THE RELATIONSHIP BETWEEN AGE AND THE ACTION OF ATROPINE AND MORPHINE

¹ From the Physiological Laboratory, Cambridge

1. The median lethal dose of atropine sulphate intraperitoneally injected in rabbits amounts to 0.225 gram per kilogram of body weight in the first month of life and to 0.35 gram per kilogram in rabbits older than one month. The increased susceptibility of very young rabbits is shown by the relatively high percentage of mortality after the injection of 0.15 gram per kilogram in rabbits in the first week of life.

2. Atropine poisoning takes a different course in young and in older rabbits. On rabbits in the first week atropine acts as a poison which merely paralyses the central nervous system. The respiratory rate is not increased, but slowed down from the beginning. Non-lethal doses of atropine have a marked narcotic effect.

Rabbits in the second to fourth weeks of life show violent clonic and tonic convulsions. They may recover even though the convulsions may continue for several hours. The older the rabbits, the more the rate of heart beat is accelerated. The narcotic effect disappears with increasing age.

In older rabbits the frequency of respiration and heart rate are markedly increased by larger doses of atropine. Only after administration of lethal doses can clonic convulsions be observed. Paralysis of respiration follows within a few minutes.

3. The median lethal dose of morphine hydrochloride intraperitoneally injected into rabbits amounts to 0.15 gram per kilogram of body weight in the first and second weeks of life, increases to 0.6 gram per kilogram in the second month, and decreases again to 0.4 gram per kilogram in rabbits older than two months.

4. In the very young rabbits the strychine-like character of the morphine convulsions is more marked than in older rabbits.

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