THE THYROTROPIC HORMONE 



duced in hypophysectomized anuran larvae. x'\dult amphibia, 

 subjected to the same operation, shed the accumulated layers 

 of cornified epidermis. Heat-production is raised to normal 

 or can be elevated above normal. 



These facts have led to efforts to attribute deficiency or 

 hyperfunction of the thyroid in man to a deficient or ab- 

 normally rapid rate of secretion of thyrotropic hormone. 

 Such an explanation, it appears, may be of value in unravel- 

 ing the genesis of certain types of hyperthyroidism in man. 

 The hyperthyroidism associated with acromegaly probably 

 is the result of the secretion of excessive amounts of thyro- 

 tropic hormone. On the other hand, thyroid deficiency in 

 man less often seems to depend upon a disturbance of the 

 anterior pituitary. 



The effects of anterior pituitary extracts containing thyro- 

 tropic hormone have been studied extensively in mammals. 

 Occasionally all the histological signs of thyroid stimulation 

 are present without the expected general physiological 

 changes, such as an elevated basal metabolic rate. Usually, 

 however, the phenomena are associated. Under suitable con- 

 ditions thyroid hormone is found to be liberated within a few 

 hours or less following the injection of thyrotropic extract and 

 acts more rapidly than its essential fraction, thyroxine, x-^n- 

 tagonistic substances such as oestrogens, thyroxine, iodides, 

 etc., appear to act in a variety of ways. Sometimes the action 

 is peripheral to the thyroid; at other times the thyroid itself 

 or the interaction between thyrotropic hormone and the 

 thyroid appears to be affected. 



Thyrotropic extracts contain both the hormone and other 

 substances. If such extracts are repeatedly injected, "anti- 

 hormone" may be produced. This phenomenon has not been 

 shown to be of physiological importance. 



Exophthalmos can be produced by the injection of anterior 

 pituitary extract into normal or thyroidectomized animals. 

 It is not known whether or not thyrotropic hormone is re- 

 sponsible for its appearance. 



i 197] 



