Effects of adrenaline and noradrenaline on the heat production of warm- and cold-acclimated sheep

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Abstract
The heat production (HP), heart rate (HR), respiration rate, rumen motility, and body temperature responses to 2.5-h adrenaline (A) and noradrenaline (NA) intrajugular infusions at 0.00, 0.15, 0.30, 0.60, and 0.90 μg∙kg−1∙min−1 were studied in 10 shorn wethers which had been chronically (3–8 weeks) exposed to warm (19–24 °C) or moderately cold (8–13 °C) temperatures. Heat production, as estimated from respired gas analysis, increased 40–45% with all doses of A and the effect was potentiated by chronic cold exposure. Only the higher dose rates of NA induced an increase in HP. The maximum HP increase due to NA was 30% and the effect was not influenced by chronic cold exposure. Thermoneutral HP was greater by 16–19% in cold-acclimated as compared with warm-acclimated sheep. Corresponding to the HP effects of A and NA, all doses of A and the highest dose of NA resulted in slight increases in rectal temperature. Respiration rate increased with increased dose rate of NA but only the highest dose of A resulted in an increase in respiration rate. HR, rectal temperature, and respiration rate responses to A and NA were not influenced by cold acclimation.