The stress syndrome in the rabbit

Abstract

(1) Adrenal weights and adrenal ascorbic acid levels in wild rabbits are very variable. (2) The number of lipoid droplets in the adrenal cortex of a wild rabbit that has been kept in the laboratory for a settling-in period is much greater than that in the cortex of an animal killed in the field. (3) A stress such as cold (-12°C) has little effect on adrenal weight, on ascorbic acid level, or on the number of lipoid droplets in the cortex. (4) A severe stressor such as formalin injected subcutaneously elicits a threefold increase in size of the adrenal. (5) Growth, haemoglobin levels, blood sugar levels, and blood urea levels are unchanged by a 20-day treatment with cold for 6-7 hours daily. Rabbits adapted to cold in this way can survive a period of 72 hours at -12'C without food or water. Untrained rabbits go into hypoglycaemic shock and exhibit uraemia within 24 hours of continuous treatment at - lZ°C. (6) Adaptation to noise gives crossed resistance to cold. Rabbits treated with formalin, which is too severe a stressor, have no resistance to cold in spite of the fact that their adrenals are large and have a full complement of lipoid granules. (7) Rabbits from dense populations are as resistant to physical stress as rabbits from populations of moderate density, provided nutrition is adequate. Lack of food leads to loss of resistance to physical stress. (8) The biochemical and morphological findings are discussed in relation to current theories of stress and regulation of animal numbers.