Plasma catecholamine concentrations of newborn piglets in thermoneutral and cold environments

Plasma epinephrine and norepinephrine concentrations were measured in seventeen unanaesthetized 3 to 4 days-old piglets while in a thermoneutral environment (31.3°C) and 30, 45 and 60 min after induction of environmental cold stress (19.9-23.1°C). Plasma epinephrine and norepinephrine concentrations in a warm environment were 142 ± 26 pg/ml, and 456 ± 44 pg/ml respectively. Environmental cold stress evoked significant increases in norepinephrine values after 30 (624 ± 58 pg/ml), 45 (626 ± 60 pg/ml) and 60 (626 ± 54 pg/ml) min of cold stress. Plasma epinephrine concentrations did not significantly change during environmental cold stress. Post-hoc stratification of piglets into normothermic (deep rectal temperature 38.6°C-38.8°C, n = 9) and hypothermic (deep rectal temperature 37.1°C-37.7°C, n = 7) subgroups revealed significant increases in plasma norepinephrine concentrations only in the hypothermic subgroup. We conclude that plasma norepinephrine, but not epinephrine, is increased in newborn piglets during environmental cold stress and that the changes in norepinephrine concentrations are related to body core hypothermia. We speculate that hypothermia-mediated reductions in peripheral norepinephrine breakdown and re-uptake contribute to the rise in circulating levels.