THE THYROTROPIC HORMONE 



form method of assay (hypertrophy of the guinea pig thyroid 

 according to Rowlands and Parkes). Two methods of initial 

 extraction of the same acetone-desiccated powders were 

 employed with the results shown in Table 5. From this data 

 it appears that the best practical sources of thyrotropic hor- 

 mone are the pituitaries of cattle and pigs.^ 



TABLE 5 



Powdered Pituitary of 



Units per Gram of Desiccated 



Powder after Initial 



Extraction with 



* Anterior lobe only. Apparently the other figures refer to whole 

 pituitary. 



The efects of the injection of pituitary extracts containing 

 thyrotropic hormone, i. Morphological changes in the thyroid 

 gland. — The response of the thyroid of different animals to 

 thyrotropic hormone probably varies widely. A good ex- 

 ample is the great susceptibility of the guinea pig's gland in 

 comparison with the insensitivity of the rat's thyroid. With 

 doses near the threshold, all parts of the gland are not equally 

 sensitive; in the thyroid of the guinea pig the first and more 

 pronounced changes due to thyrotropic hormone are observed 

 in the central part of the thyroid lobes. Compensatory hy- 

 pertrophy of the thyroid following partial extirpation de- 

 pends upon the secretion of thyrotropic hormone by the an- 

 terior pituitary. Albani's recent report (1936) indicated that 

 in young dogs this may be a very slow process, different from 



* The anterior pituitary of the ox contains a higher concentration of thyrotropic 

 hormone than that of the guinea pig (Emerson, 1937); however, the rat's gland con- 

 tains 7-9 times as much as that of the ox (McQueen- Williams, 1935). 



[181I 



