194 P. A. Desaulles 



response and concomitantly higher sodium excretion with 

 advancing age, especially in females. 



This, together with the similarity of the changes in the 

 sodium/potassium ratio induced by aldosterone and Cortisol 

 during these experiments, even if the factors of ageing and sex 

 act differently on them, underlines certain similarities of effect 

 in a number of known adrenal steroids which have already 

 been stressed (Meier and Desaulles, 1956; Gaunt and Chart, 

 1958). Relative dosage, time, age, experimental conditions 

 and different stages of homeostasis are among the factors 

 modifying these similar patterns of effect. The relation of 

 homeostasis to the development of the animal organism is too 

 complex to permit of any definite statement. We have 

 simply tried to show that the properties of certain hormones 

 may be profoundly affected by such factors as sex difference 

 and increasing age, and that these differences may act in the 

 same or in quite different ways and thus contribute towards 

 a better understanding of pathophysiological changes due to 

 age. 



Summary 



It has been shown that in rats of differing age and sex the 

 sensitivity to the influence of aldosterone and Cortisol on 

 urinary electrolyte excretion varies greatly. 



Whereas age tends to increase sensitivity of the animals to 

 the effects of aldosterone, their sensitivity to Cortisol by way 

 of contrast tends to diminish. 



On the other hand, female animals show a greater respon- 

 siveness to these changes than male animals. 



These results are discussed. 



Acknowledgement 



I should like to express my thanks to Mr. H. D. Philps (MA. Cantab.) 

 for his kind assistance in the preparation of the English text of this paper. 



REFERENCES 



Bush, I. E. (1953). Ciba Found. Colloq. Endocrin., 7, 210. London: 



Churchill. 

 Cole, D. F. (1957). Endocrinology, 60, 562. 



