Sweating in the kangaroo: a cooling mechanism during exercise, but not in the heat.

DAWSON, TERENCE J., DAVID ROBERTSHAW, AND C. RICHARD TAYLOR. Sweating in the kangaroo: a cooling mechanism during exercise, but not in the heat. Am. J. Physiol. 227(Z) : 494498. 1974.-The red kangaroo (Megaleia rufa) uses three evaporative cooling mechanisms : panting, sweating, and saliva spreading. Sweating only occurs during exercise. Resting kangaroos pant and spread saliva when faced with severe thermal load. We compared the heat balance of kangaroos resting at 24OC with that of animals hopping on a treadmill at a speed of 4 km. h-l. During this exercise heat production was approximately 8 times as great as at rest. About 43 y0 of the heat was lost by evaporation, 14% nonevaporatively, and approximately 43% was stored. Sweating accounted for 60% of the evaporative loss and respiratory evaporation accounted for about 40y0. The large increase in respiratory evaporation appeared to be due to increased respiratory ventilation required for the higher oxygen uptake. Salivation occurred during exercise, but spreading was not possible. Sweating declined and rapid panting commenced immediately when exercise ceased. Sweating appeared under the control of adrenergic neurons, the receptors being a-receptors. There was no evidence for the involvement of the adrenal medulla in sweating.