REGULATION OF GROWTH 



sectomized animal. According to Reiss, Schwarz, and Fleisch- 

 mann (1936), the administration of growth-promoting ex- 

 tract (containing some adrenotropic but no thyrotropic or 

 gonadotropic hormone) to the starved dog or rabbit causes, 

 even after a few hours, a considerable fall in the "rest" N 

 (10-49 P^^ cent) and free arginine (19-43 per cent) associated 

 with a rise of 21-66 per cent in the urea N of the blood. Their 

 results are not fully in accord with those previously reported 

 by others. In a study of the phosphatase activity of bone and 

 kidney, Wilkins and others (1935) were unable to detect any 

 significant difference in adult female rats, some of which re- 

 ceived injections of a potent growth-promoting extract. 

 Body, bone, and kidney weights were all increased as a result 

 of the treatment. 



The relationship between the growth-promoting hormone and 

 other glands of internal secretion, i. The gonads J — Perhaps 

 the simplest interpretation of the effect of gonadectomy on 

 growth in certain animals is that the effect is principally due 

 to a change in the secretory activity of the anterior pitui- 

 tary. Recently, studies of growth-alterations following gonad- 

 ectomy in the rat have been reported by Holt, Keeton, 

 and Vcnnesland (1936), Billeter (1937), Freudenberger and 

 Hashimoto (1937), and Freudenberger and Howard (1937). 

 Castrated and normal male rats gow at about the same rate; 

 however, the normal male tends to grow larger. The spayed 

 female rat clearly grows more rapidly and maintains its 

 weight better than the normal female. The difference is not 

 due to the deposition of fat and may amount to 20 per cent 

 at an age of 13 weeks (9 weeks after spaying). The glands of 

 internal secretion as well as other viscera are heavier; the 

 most striking change is in the thymus which may be 75 per 

 cent heavier than that of the normal female. 



iAt least in the case of the female rat, the internal secre- 



i Growth-promoting extract, like others derived from the anterior pituitary, may 

 contain a substance inhibiting certain gonadotropic effects. This substance has been 

 named "pituitary antagonist" by Evans and is discussed in chap. iii. 



[39] 



