76 Discussion 



and not just filtered from the plasma. One then wonders whether epith- 

 elium does not similarly push out potassium in exchange for the sodium 

 which is being reabsorbed — the sort of mechanism that is possibly under 

 aldosterone control. 



I believe that although Conn has concentrated mainly on sweat in his 

 tests for aldosterone activity, he has also used saliva in a similar way. 

 With a rice diet we did not get any falling off in the sodium concentration 

 in the saliva, as far as we could determine. 



Thaysen : An exchange mechanism between sodium and potassium ions 

 at the site of sodium reabsorption is certainly a very likely possibility. 

 This may be one factor causing the potassium concentration of the final 

 secretory product to exceed that of the plasma. However, glands which 

 apparently possess no sodium-reabsorbing mechanism may also have a 

 potassium concentration in their secretions, exceeding the plasma potas- 

 sium concentration. This applies, for example, to the lachrymal (Fig.l, 

 p. 63) and the sublingual glands (Lundberg, 19576). Therefore I believe 

 that two factors may be at stake. First, the presecretion is frequently 

 formed with a potassium concentration which exceeds that of the plasma 

 (and a correspondingly lower sodium concentration). Second, in some 

 glands additional potassium ions are added to the presecretion in ex- 

 change for reabsorbed sodium ions. Similarly, the adrenal steroids may 

 have a dual site of action in the glands. In contradistinction to the situa- 

 tion in the glomerular nephron, adrenal steroids may act on the gland 

 cells forming the presecretion and thus alter the Na/K ratio of the pre- 

 cursor, and they may act on the cells in the ducts which reabsorb sodium 

 ions from the presecretion in exchange for potassium ions. There is some 

 evidence indicating such a dual site of action of aldosterone on the glands 

 (Thorn et al. (1954). Fed. Proc, 13, 310), but I do not know of any con- 

 clusive experiments. One way of approaching the problem may be to 

 compare the effect of aldosterone on glands with and without a sodium- 

 reabsorbing mechanism, e.g. on the sweat or parotid gland as contrasted 

 with the lachrymal or pancreatic. 



As regards your comment about the rice diet, sodium depletion, in- 

 duced by a low sodium diet, causes the concentration of sodium to 

 decrease and the concentration of potassium to increase in sweat as well 

 as in saliva (McCance, R. A. (1938). J. Physiol, 92, 208). However, the 

 response of the glandular epithelium to sodium depletion is both delayed 

 and incomplete as compared to that of the kidney tubule (Robinson et 

 al. (1955). J. cqypl. Physiol., 8, 159; Thorn et al. (1956). J. appl. Physiol, 

 9, 477). 



Karvonen: Can anyone comment on the statistical finding that men 

 have lower sodium and potassium than women in their sweat, and that 

 the Na/K ratio in women is significantly lower than in men (Ahlman et 

 al (1953). J. clin. Endocrin. Metab., 13, 773)? 



Desaulles: That is a very interesting challenge. We have similar 

 findings in animals, not in sweat but in urine, but I have absolutely no 

 explanation for it. It is just an observed fact. 



Talbot : I wonder if those who are commenting on the sodium, chloride 

 and potassium concentrations in sweat all have in mind the relationship 



