2. Endocrines and Populations 211 



mciit of neonatal rats can also result in marked morphologic changes in 

 the brain and skull (INIoss, 1955). Cortisone or hydrocortisone may stimu- 

 late lactation (Selye, 1954), but the mechanism by which this is accom- 

 plished is unknown. These effects cannot be attributed to an inhibition of 

 the secretion of gonadotropin by cortisone, as it has been shown that even 

 relatively large doses of cortisone are without effect on the production of 

 gonadotropins (Byrnes and Shipley, 1950), although it is well known that 

 enormous doses of corticoids do exert some antigonadotrophic activity. 



The carbohydrate-active corticoids also involute lymphoid tissues by 

 producing degeneration and actual fragmentation of the lymphoid cells, 

 inhibition of differentiation, and depression of lymphocytopoiesis (Selye, 

 1950; Dougherty, 1953; Santisteban and Dougherty, 1954; Gordon, 1955; 

 Weaver, 1955). These effects are also seen following injection of ACTH, 

 with an increase in endogenous corticosteroid secretion (Baker ei al., 1951). 

 Lj^mphocytolysis evidently serves to release a readily available store of 

 amino acids and may serve to provide a sudden flood of stored antibodies, 

 which are normally produced m the lymphoid tissues (Keuning et al., 

 1950; Dougherty, 1953; Kass et al., 1953a; Sundberg, 1955). These actions 

 result in involution of the thymus, lymph nodes, and malpighian corpuscles 

 of the spleen. Therefore weights of those organs may provide useful indices 

 of adrenocortical activity when they are used along with other indices of 

 adrenal activity, such as adrenal weight, and appropriate controls. It 

 should be remembered, however, that androgens, and to a somewhat lesser 

 extent estrogens, are capable of involuting the thymus (Burrows, 1949; 

 Weaver, 1955) ; therefore cognizance must be taken of this fact when using 

 thymic involution as a means of appraising adrenocortical activity. How- 

 ever, the lymph nodes lose weight only after treatment of the animal with 

 ACTH or carbohydrate-active corticoids (Weaver, 1955). Estrogen, tes- 

 tosterone, thyroid extract, adrenalectomy, thyroidectomy, and gonadec- 

 tomy were without effect on the lymph nodes in these experiments (Weaver, 

 1955) . The adrenal carbohydrate-active corticoids also depress the numbers 

 of circulating eosinophils and lymphocytes, so that counts of these cells are 

 frequently used to assess the functional integrity of the pituitary-adreno- 

 cortical system (Speirs and Meyer, 1949; 1951; Gordon, 1955; Speirs, 

 1955). In using counts of eosinophils or lymphocytes as indices of adreno- 

 cortical activity in wild mammals care must be taken (1) to standardize 

 the procedures so that the results are completely comparable from count 

 to count, and (2) not to elicit an adrenocortical response during the process 

 of handling the animal. 



The biological activity of ll^-hydroxyA^-androstene-3,17-dione (llOH- 

 4AD) and the closely related steroid 11/3-hydroxytestosterone, as well as 

 other related C19 steroids, deserve further comment, as one or the other of 



