CHAPTER VI 



THE THYROTROPIC HORMONE 



ONE of the impressive effects of hypophysectomy in 

 mammals is a marked fall in the rate at which heat 

 is produced. This change is due principally to in- 

 adequate function of the thyroid gland and can be correlated 

 with morphological changes in the thyroid — i.e., undis- 

 charged colloid accumulates in vesicles lined by flat, "in- 

 active," epithelial cells. A specific substance called the thy- 

 rotropic hormone is secreted only by the anterior pituitary;^ 

 it is responsible for the maintenance of normal thyroid func- 

 tion and may be important in disorders attributed to deficient 

 or excessive thyroid secretion. In classes of animals other 

 than mammals different changes, likewise dependent on the 

 virtual absence of thyroid secretion, follow the removal of 

 the pars glandularis. A well-known example is the absence 

 of metamorphosis after the removal of the gland from anuran 

 larvae. 



The thyrotropic hormone has not been isolated as a pure 

 substance. Nearly all the recent progress is concerned with 

 its biological action. 



The biology of thyrotropic hormone in fishes^ amphibia^ and 

 reptiles. — Young and Bellerby (1935) were not successful in 

 attempts to produce metamorphosis in lampreys {Lampetra 

 planeri) by the injection of an extract of the anterior pitui- 

 tary of the ox. 



The pioneer work of Adler, Smith, and Allen clearly dem- 

 onstrated that metamorphosis in anuran amphibia is pre- 



' Sturm and Schoning (1935) believed that extracts of the ovary or the medulla 

 of the adrenal gland may act like true thyrotropic hormone. Repetition of their 

 work with ovarian tissue yielded no confirmation (Ballif and Gherscovici, 1936; 

 McGinty and McCullough, 1936; and Emerson, 1937). 



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