Hypergravitation and sympatho-adrenergic reactivity.

The sympatho-adrenergic reaction of the organism subjected to hypergravitation was investigated in rats exposed to +6 Gz. The electro- and cardiotachograms recorded telemetrically were correlated with the adrenal catecholamine content. The determinations were made in controls and in rats treated with hexamethonium and atropine administered separately or together. The rats reacted to acceleration initially by a short bradycardia followed by tachycardia. In one case there was a sustained bradycardic response. Hexamethonium (C6) lowered the resting heart rate, attenuated the initial bradycardia and reduced the consecutive tachycardia. In some rats during centrifugation a bradycardic and arhythmic response was found sometimes ending in cardiac arrest. Hexamethonium stored the catecholamines in the adrenals as a result of their increased concentration. Atropin brought about resting tachycardia, disappearance of bradycardia from the very beginning of centrifugation and a more accentuated tachycardia. Atropin and hexamethonium administrated together diminished the response to acceleration.