I n a previous communication (Koneff, '44) it was reported that injection of adrenocorticotropic hormone into normal young male rats caused diminution in weight of the hypophysis, definite decrease in size of basophils accompanied by loss of granular material, and changes in the nucleus and cell organelles. These alterations were interpreted as indicative of retarded or depressed functional activity of the basophils. No significant changes were observed in the acidophils.
Recent biological studies conducted here have indicated that the effect of ACTH in adrenalectomized rats is different from that in normal males.2 Namely, it does not retard the body weight increase in the absence of the adrenals, causes no decrease in thymus or thyroid weight (Simpson, Li, Reinhardt and Evans, '43) and does not alter histologically the testis in the adrenalectomized animal. It was of interest, therefore, to see whether the morphological appearance of the anterior pituitary would also differ in normal and adrenalectomized ACTH-treated rats.
NATERIAL AND METHODS
As in the previous investigation of the effect of ACTH on the anterior hypophysis, young male rats were used. The rats were adrenalectomized at 26 days of age and injections of pure ACTH (Li, Evans and Simpson, '43) were begun immediately. One milligram doses (divided into three injections) were given daily intraperitoneally for 30 days.
Aided by grants from the Rockefeller Foundation, the Josiah Macy, J r . Foundation and General Mills, Inc. I wish to express my thanks to Prof. Herbert M. Evans and Dr. Miriam E. Simpson for their assistance and f o r tho use of the facilities of the Institute of Experimental Biology.
"he report from the Institute concerning the biological effects of the ACTH in young adrenalectomized rats will be published separately.