Thermoregulatory responses to tyramine in the pigeon

Intravenous injections of different doses of tyramine induced hypothermia in the pigeon in the cold and a moderate hyperthermia in the warm environment. The hypothermia was correlated with a dose-dependent decline in shivering. Hyperthermia was attributed to the chrono- and inotropic effects of tyramine. The indirect stimulatory effects of noradrenaline (NA) at the tissue level were studied. Pretreatment with alpha-methyl-para-tyrosine (alpha-MpT) and blocking alpha-adrenoceptors with phentolamine, diminished the hypothermia induced by tyramine in the cold. The results obtained indicate that the release of endogenous NA stimulated by tyramine might result either in hypothermia or hyperthermia, thus resembling similar effects obtained with exogenous NA in birds.