240 /. /. Christian 



reproductive function. However, a great deal more investigation is neces- 

 sary to clarify thyroidal-adrenal-gonadal relationships. 



6. Other Thyroid Relationships 



In addition to its relationship to the adrenals and gonads and to its 

 general metabolic effects, the thyroid hormones play specific roles in the 

 maintenance of other organs, and these may offer means of evaluating 

 thyroid function in intact mammals in the field, providing they are used 

 in conjunction with other information. For example, the harderian glands 

 of rats and mice are maintained by thyroid hormones and as yet unknown 

 pituitary factors (Boas and Bates, 1954; Hellman and Collins, 1957), al- 

 though the thyroid may not be essential for the maintenance of these 

 glands in guinea pigs (Smelser, 1943). Thyroid hormone, in conjunction 

 with androgens, is required for the maintenance of the size and granulation 

 of the cells of the serous tubules of the submaxillary glands of male rats 

 (Grad and Leblond, 1949) . The thyroid alone restores the number of these 

 cells to normal, but does not affect the size or granulation. 



Thyroid function in general declines moderately with age and increased 

 size (Hurst and Turner, 1947), but there are no marked effects of this 

 decline on growth or other functions. 



It should be clear from the above account that the thyroid and its 

 hormones participate actively in the adaptive responses and probably play 

 a significant role in many aspects of these responses. Investigations on the 

 reactions of the thyroid with changes in the size of mammalian populations 

 and its relationship to adrenal and reproductive functions are needed. 



C. Other Endocrine Adaptive Factors 



1. Pancreatic Islets 



A discussion of the physiology of the pancreas with respect to glucose 

 metabolism is not properly the function of this chapter, but it should be 

 mentioned as one of the important endocrine organs regulating glucose 

 utilization. The hormone best known of the islets of Langerhans is insulin, 

 which is derived from the beta cells. More recently glucagon, presumably 

 from the alpha cells, has been described. Insulin, in brief, increases the 

 utilization of glucose and in many of its actions is antagonized by cortisone. 

 Glucagon, on the other hand, is a hyperglycemic factor. The function of 

 these hormones wdth respect to the generalized adaptive responses has been 

 little studied, but they certainly must play an important part in the general 

 economy of the mammal under adverse circumstances. Anything affecting 



