BLOOD AND PITUITARY ACTH IN INTACT AND ADRENALECTOMIZED RATS AFTER STRESS1

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Abstract
The concentration of ACTH in the blood of the non-stressed intact rat is too low to be detected by the technique employed and is estimated to be less than 0.5 milliunit/ 100 ml. One week after adrenalectomy the concentration has increased to 3.2 milliunits/100 ml. Two minutes after application of a stressful stimulus (exposure to ether for 45 seconds or exposure to ether plus a standardized scald), ACTH is detectable in blood of the intact rat. The mean concentration is estimated to be 1 milliunit/100 ml. These same stresses applied to the adrenalectomized rat induce a two - threefold increase in blood ACTH over non-stress levels. Six minutes after exposure to ether plus a standardized scald, ACTH is not detectable in the blood of the intact rat, but is present in high concentration in the adrenalectomized animal. Continuous exposure to ether plus exsanguination induces a significant increase in the blood-ACTH titer of the intact rat. The mean concentration of ACTH is estimated to be 2.6 milliunits/100 ml. The blood-ACTH titer of the adrenalectomized rat similarly stressed is not significantly different from that of the adrenalectomized rat exposed to ether alone. It is concluded that: (1) Accelerated release of ACTH occurs immediately after application of stressful stimuli. (2) The concentration of adrenocorticosteroids in blood and/or tissues exerts the dominant role in regulating pituitary ACTH. (3) A hypothalamic factor may initiate pituitary discharge of ACTH following the application of stressful stimuli. The ACTH content of pituitary obtained from the non-stressed or from the stressed intact rat is approximately 70 milliunits. Two weeks after adrenalectomy the mean content has increased to 170 milliunits. There is no significant difference between the ACTH content of pituitary obtained from non-stressed adrenalectomized and from stressed adrenalectomized animals. However, the increased rate of discharge which follows stress may have resulted in a decrease in pituitary stores which could not be detected by the assay technique.