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THE PITUITARY GROWTH HORMONE: 

 SOME PHYSIOLOGICAL CONSIDERATIONS* 



Ernst Knobil 



HARVARD MEDICAL SCHOOL 



The term growth, while seemingly benign to the cellular biologist, has 

 awesome and forbidding implications to the mammalian physiologist, 

 who, though armed with the tantalizing array of information forged by 

 biochemists and microbiologists, is, more often than not, constrained to 

 observe a proverbial "black box." He chips away as best he can with 

 rough tools in the hope of finding a weak spot in the "box" v/hich will 

 yield to the assault of a more sophisticated and delicate armamen- 

 tarium, which in turn may reveal the processes that transform a small, 

 immature individual into a fully grown one. For lack of a more useful 

 definition, he terms such a transformation "growth." The black box has 

 yielded to a rough tool, the surgeon's knife, and a weak spot has been 

 exposed for further attack: the experimental arrest and restoration of 

 growth. 



Role of the pituitary gland 



Removal of the pituitary gland during appropriate stages in the 

 development of various vertebrates, from fish to man, results in a strik- 

 ing decrease or, more often, in a complete arrest of somatic growth and 

 development. This result of hypophysectomy is best illustrated by a 

 simple experiment. The monkey on the left (Figure 1) was hypophy- 

 sectomized in June, 1958, when he weighed 2.7 kg. At that time the 

 unoperated control on the right weighed 2.9 kg. The photograph was 



* The studies herein reported that originated in the author's laboratory were 

 supported by grants from the United States Public Health Service and the Amer- 

 ican Cancer Society. 



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