Cold stress of the mammal, bird and reptile

Abstract

1. (1) A rise in plasma sodium and haemodilution occurs on short-term (48 hr) cold exposure (0°C) in the pigeon. These shifts are similar to those recorded for the intact rat but more rapidly to normal. The changes are in agreement with a theory of increased mineralocorticoid activity resulting from the acute cold stress and the more rapid adaptation of the pigeon compared with the rat is in line with its greater resistance to cold. 2. (2) There is a haemodilution in reptiles on similar short-term cold exposure but both plasma sodium and potassium levels fall. This contrasts with the response of the rat and pigeon. 3. (3) In the rat on long-term (4–20 weeks) cold exposure (0°C) the plasma sodium and potassium levels are high but associated with haemodilution. These changes are accompanied by a slight fall in body temperature and pathological changes including tissue breakdown. There is a doubling of adrenal weight and histological signs of kidney and adrenal cortical damage. 4. (4) The pigeon on long-term (2–10 weeks) cold exposure (0°C) does not show similar changes. Plasma sodium and potassium are just below normal but again there is haemodilution. There is no fall in body temperature and the birds maintain good health with no gross pathological or histological abnormalities. The adrenal cortex shows no increase in size or weight. 5. (5) These results suggest that the long-term cold exposure of the intact rat may be associated with an elevated mineralocorticoid level and the cold stress produces changes similar to long-term dosage of sensitized animals with mineralocorticoids. The pigeon by contrast does not respond to a similar degree of long-term cold stress, but only shows haemodilution.