Hormonal determinants of mammalian tolerance to acceleration stress

¹ Aviation Medical Acceleration Laboratory, U.S. Naval Air Development Center, Johnsville, Pennsylvania

The pituitary-adrenal hormonal axis has been implicated as a critical factor in the survival of the rat to acceleration stress. The physiological end point for the tolerance of animals to high positive acceleration stress was obtained by determining the time to reduce the heart rate from 8 to 2 beats/sec. at 20 g. With this technique, a significant increase (300%) in the survival time of rats to 20 g was found following hypophysectomy. A significant loss (60%) of tolerance to high acceleration stress was found in adrenalectomized rats. The procedures of hypophysectomy plus adrenalectomy apparently opposed the effect of each operation alone in the rat to yield an animal that tends to approach the normal rat in its ability to tolerate acceleration. A significant drop in the tolerance to acceleration of hypophysectomized rats was found 7 and 15 weeks after operation compared to that found with the animals 3 weeks after hypophysectomy and a significant increase in the tolerance of the adrenalectomized rat was found 11 weeks after operation compared to the tolerance at 5 weeks after adrenalectomy. In both operated populations, the direction of change was toward the tolerance level of the normal rat.

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(With the Technical Assistance of Anne Zella)