The Biology of Senescence 



alive. Compared with the more gradual disappearance of ova 

 in other mammals, the human menopause is unusually complete 

 and sudden. The range of this phenomenon among primates 

 is not at present known. Nobody has seen a postmenopausal 

 monkey (Krohn 1955). 



There is some cause for regarding gonadal senescence and 

 the group of effects which follow senile gonadal withdrawal as 

 a separate 'senescence' from that of the animal as a whole, since 

 gonadal supplements can reverse a whole series of subsidiary 

 senile changes without materially reversing the progress of 

 somatic senescence judged by survival. In the castrated male 

 mammal, gonadal hormone supplements may perhaps actually 

 shorten life. There is no demonstrable androgen deficiency in 

 normal senile male rats (Korenchevsky, Paris and Benjamin, 

 1953), nor, probably, in most old men. 



Although sex hormones do not rejuvenate the organism in the 

 manner envisaged by writers such as Voronoff, they produce a 

 closer approach to 'rejuvenation', covering more structures and 

 body processes, than do any other hormones which have been 

 investigated. In addition to their effects upon the secondary 

 sexual characters, such as beard growth (Chieffi, 1949) or 

 structure of vaginal epithelium (Loeb, 1944; Allen and Masters, 

 1948) and upon the genitalia themselves, androgens (Kenyon, 

 1942; Kochakian and Murlin, 1931; Kochakian, 1937) and 

 probably also oestrogens (Kenyon, 1942) exert an important 

 'anabolic' effect with nitrogen retention and increased protein 

 synthesis, and produce a number of unexpected peripheral 

 changes, generally in the direction of a restoration of 'young' 

 structure (Korenchevsky, Paris and Benjamin, 1953). Thus 

 oestrogens have been stated to produce a striking reversal of the 

 atrophy of the senile nasal mucosa (Kountz, 1950) and cer- 

 tainly produce extensive changes in senile skin, with dermal 

 regeneration (Goldzieher and Goldzieher, 1950; Chieffi, 1950a) 

 and restoration of elasticity (Chieffi, 1951). That the pos- 

 sibility of 'rejuvenation by replacement' is limited, even where 

 the reproductive organs are concerned, is shown by Kirk's 

 failure (1948, 1949) to restore the phosphatase activity of senile 

 prostatic secretion with androgens, although this activity is so 

 restored in young hypogonadal males. 



178 



