The Biology of Senescence 



Characteristic variations in hormone output occur through- 

 out the mammalian life cycle; they are of two types — cyclical 

 and secular. These changes are the biochemical equivalent of 

 the sudden movements of embryonic tissue which are seen in 

 speeded-up films of developing organisms — they are part cause, 

 part effect, and they represent only the outward and visible 

 manifestation of changes in the quality and quantity of cell 

 response. The hormones most likely to be linked directly with 

 the senile process, such as the growth hormone of the pituitary, 

 cannot be estimated in the intact animal. Of those which can 

 be so estimated, the group of 1 7-keto-steroids show a decline 

 which continues with the rise of the force of mortality 

 (McGavack, 1951; Kirk, 1949; Hamburger, 1948; Robinson, 

 1948; Hamilton and Hamilton, 1948; Hamilton, Hamilton and 

 Mestler, 1954 (Fig. 41) ). The concept of an 'adrenopause 5 

 analogous to the menopause seems to have little to support 

 it at present. Apart from this, there is no single hormonal 

 change which correlates with senescence, no single endocrine 

 organ, of those which can be removed without fatal results, 

 whose extirpation produces the syndrome of senility in mam- 

 mals; and no hormone or combination of hormones which 

 is known to produce more than a limited, and apparently 

 secondary, reversal of senile changes. Ablation of a gland is not 

 the same thing as its senescence in situ, and in surgical castration 

 for prostatic and mammary cancer there is evidence that inter- 

 conversion may take place between adrenal and gonadal 

 steroids, but no simple hypothesis that senescence is a 'with- 

 drawal' effect is substantiated by the existing experimental 

 evidence. It appears that the sequence of developmental changes 

 in endocrine activity which ends in senescence cannot so far be 

 made to run backwards by hormone supplements, except in a 

 very minor degree. 



In a long series of studies, Korenchevsky (e.g. Korenchevsky 

 and Jones, 1947, 1948; Korenchevsky, Paris and Benjamin, 

 1950, 1953) has tried to show how far hormone supplements can 

 reverse the senile process, judged by the restoration of the 

 relative hypoplasia of organs. A great many of the senile 

 structural changes described in endocrines are closely paralleled, 

 though at a lesser level of severity, by the changes in structure 



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