Cortico-Adrenal Insufficiency in Rats Under Reduced Pressure

Abstract

This report concerns one of the aspects of a broader research project in which a fairly comprehensive study was made of the response of rats to reduced pressure, inclusive of the relation of such response to some pathological conditions both in rats and other animals. By experiments carried out under a variety of standardized levels of low pressure and for a series of standardized periods of exposure to such pressures, it has been shown that various functional factors respond in a uniform and typical manner to these environments. On this evidence 3 stages could be distinguished with respect to the total exposure period of a rat to the low pressure environment: (a) a pre-adaptive stage during which most deviations of values indicate an unfavorable effect, (b) an adaptive stage during which deviations occur in the opposite direction and are indicative of adaptive adjustments, and (c) a post-adaptive stage during which functional shifts occur again in a direction suggesting pathological changes. The third of these stages was found to occur mainly when the animals were exposed for extended periods to very low levels of pressure and was considered to be an expression of an exhausted adaptive function.

It was considered also that the functional changes occurring during this third stage would be the most promising material for suggesting the nature of the general functional state which is produced by artificial and possibly also natural altitude conditions. For this purpose the total picture of physiological effects found during this stage was compared with the syndromes of various pathological conditions of known etiology. It was discovered that the functional alterations under these particular low pressure conditions are identical with the functional alterations resulting from corticoadrenal insufficiency in adrenalectomized animals. Some earlier observations, viz., the sudden and unexpected deaths of apparently normal rats and the finding of intestinal hemorrhages in many of these rats, supported the assumption that the adrenal activity is involved in the deterioration of animals in this abnormal “climate.” It was reasoned that if some direct proof could be obtained for the correctness of this assumption it would become useful later for relating acclimatization to altitude with the function of the adrenal cortex. It was the purpose of this particular investigation to furnish such experimental proof.