EFFECTS OF ACUTE COLD EXPOSURE ON PLASMA CONCENTRATIONS OF NORADRENALINE AND ADRENALINE IN SHEEP

Abstract

Six acute cold trials were performed with mature wethers shorn to a fleece depth of 5–10 mm and maintained in a controlled environment chamber. Heart rate, hematocrit and plasma concentrations of glucose, noradrenaline (NA) and adrenaline (A) were measured during each trial which consisted of a 90-min period at 25 °C, a 150-min period of cold stress (to −19 °C) and a 120-min warming period. All measurements and samples were taken from outside the controlled environment chamber by means of extended conduits to minimize animal disturbance. Mean values at 25 °C were: heart rate 69 beats/min, hematocrit 26.7%, plasma glucose 62 mg/100 ml, NA 0.24 ng/ml and A 0.07 ng/ml. By 120- to 150-min cold exposure, mean values of all variables had increased (P < 0.001) to: heart rate 223 beats/min, hematocrit 33.1%, plasma glucose 115 mg/100 ml, NA 1.11 ng/ml and A 0.24 ng/ml. Following cold exposure, mean values of all variables returned toward pre-cold period values as chamber temperature approached 25 °C. A seventh trial performed at constant temperature (24 °C) demonstrated the marked elevation in plasma catecholamine concentrations when an experimental animal was disturbed. These trials demonstrated: (a) that plasma NA and A concentrations in resting unrestrained ruminants are similar to those of other animals in the same state, (b) that it is important to minimize animal disturbance while studying catecholamines, and (c) that he sympatho-adrenal medullary system is involved in the physiological response of sheep to acute cold stress.