SUMMARY

The concentration of adrenocorticotrophic hormone in the blood of rats was estimated at various time intervals after the removal of the adrenal glands. The hormone was not detectable until 10 days after the operation. Its concentration rose to a maximum value 3 weeks after adrenalectomy and this high circulating level was maintained for at least another 2 weeks. There were no significant differences between the results obtained using hypophysectomized and hydrocortisone-treated rats for the bioassay procedures. Direct estimates of the concentration of adrenocorticotrophic hormone (ACTH) in the blood of adrenalectomized rats have produced conflicting results. Gemzell, Van Dyke, Tobias & Evans [1951] showed that bilateral adrenalectomy in the rat resulted in an immediate and progressive increase in the circulating level of ACTH. Sydnor & Sayers [1952, 1953, 1954] and Sydnor [1955] found that the level of ACTH in the blood of adrenalectomized rats was considerably greater than that of the intact animal. On the other hand, Barrett & Hodges [1956 a] were unable to demonstrate any difference in plasma ACTH concentration between normal and adrenalectomized rats 3, 6 and 12 days after the removal of the adrenal glands. The present investi