CONCERNING THE HYPERSENSITIVITY OF ADRENALECTOMIZED RATS TO VASCULAR STRESS1

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Abstract
The amt. of blood capable of being withdrawn in a standardized acute exsanguination (bleeding vol.) is reduced significantly in salt-treated adrenalectomized rats. This difficulty in blood mobilization appears to be the effect of a deficiency in a cortico-adrenal hormone since DCA raises the bleeding vol. of adrenalectomized rats to normal levels, but is without influence on the bleeding vol. of normal animals. In interpreting the significance of these findings the conclusion is drawn that lowered bleeding volume reflects a decreased venous return and cardiac output in bled adrenalectomized rats since the lowering of bleeding vol. cannot be ascribed to decreased blood volume, decreased interstitial fluid transfer, or to possible effects of the pressure of the arterial circulation. The absence of heart failure or lung congestion, and the failure to observe bleeding from the cut heart of adrenalectomized rats after bleeding vol. has been detd. are strong evidence that the decreased bleeding vol. is primarily due to reduction of venous return. This would mean that the adrenal cortical hormones are involved in the operation of compensatory venopressor mechanisms. The significance of a primary failure of a venopressor mechanism as an explanation for the hypersensitivity of adrenalectomized animals to vascular stress has been discussed.