The sympatho-adrenergic response in hyperthermia.

The sympatho-adrenergic reaction was investigated in heated rats under the influence of a ganglioblocking agent--hexamethonium. The overheating at a 40 degrees environmental temperature produced in a relatively short interval (after 157 min on an average) the death of the animals. An initial bradycardia was followed by a tachycardic phase. In the prelethal phase there appeared bradyarrhythmia produced by conductibility troubles and activation of ectopic ventricular centers. The survival time was not influenced by hexamethonium in spite of its hypothermic action. In blood, heating produced an increased concentration of noradrenaline and adrenaline. Hexamethonium, which reduced the rectal temperature, markedly decreased both blood catecholamines concentration. On this background heating likewise produced a relative increase of both blood catecholamines content. The catecholamines changes in adrenal glands presented less significant modifications.