Influence of increased catecholamine levels in blood plasma during cold-adaptation and intramuscular infusion on thresholds of thermoregulatory reactions in guinea-pigs

Catecholamines and some of their metabolites were determined in urine and blood plasma of guinea-pigs before, during and after acclimation to a cold or warm environment. During adaptation to 5°C the amounts of noradrenaline in plasma and 24-h urine samples continuously increased up to 600% compared with values obtained at an ambient temperature of 22°C. Higher levels of dihydroxyphenylglycol and 3-methoxy-4-hydroxyphenylglycol further indicated an increased turnover of noradrenaline during cold adaptation. Acclimation to an ambient temperature of 28°C reduced the peripheral release of noradrenaline in comparison to the release observed at 22°C. Cold-induced increases in metabolic rate and electrical muscle activity both occur at a considerably lower mean body temperature in cold-than in warm-adapted guinea-pigs. The shift of thermoregulatory cold defence reactions to a lower mean body temperature could also be observed in warm-adapted animals after intramuscular infusion of noradrenaline in amounts comparable to those released during cold adaptation.