38 Paul Fourman and Patricia M. Leeson 



The position of these centres in the nervous system suggests 

 that their control involves more than a response to changes 

 in tonicity, and some purely nervous stimuli such as pain and 

 emotion may initiate, or inhibit, thirst or antidiuresis. 



A fall in the volume of the ECF can stimulate thirst and 

 antidiuresis, presumably through nervous pathways (see 

 Rosenbaum, 1957; Strauss, 1957). Smith (1957) has dis- 

 cussed at length where the receptors for the stimulus to anti- 

 diuresis might be : some of them may be in the left auricle of 

 the heart (Henry and Pearce, 1956). 



Hypernatraemia 

 Water deficiency 



Normally, thirst and antidiuresis are stimulated by a very 

 small increase in extracellular tonicity, less than two per cent 

 (Wolf, 1950; Verney, 1957). A concentration of sodium ([Na]) 

 in the plasma exceeding 150 m-equiv./l. may certainly be 

 regarded as abnormal. In a study of water deficiency pro- 

 duced experimentally in dogs, values of 160, and in one 

 animal that died a value of 186 m-equiv./l., were found 

 (Elkinton and Taffel, 1942); in a man made water-deficient 

 by Black, McCance and Young (1944) the [Na] rose to 160 

 m-equiv./l. In a patient from Texas reported by Gordon and 

 Goldner (1957) a value as high as 192 m-equiv./l. was reported. 

 He recovered. 



The "dehydration reaction". The hypernatraemia of 

 water deficiency is not simply the result of the blood becoming 

 more concentrated, for in spite of the high blood level of 

 sodium there may be very little sodium in the urine; it is 

 retained in the body. 



Allott (1939), who first drew attention to the problem of 

 hypernatraemia, found the urinary [Na] ranged from 2-5 to 

 9 m-equiv./l. in four of his patients. It now seems most likely 

 these low concentrations of sodium were a result of the 

 "dehydration reaction" first described by Peters (1948, 1952). 

 The mechanism of this reaction is not clear, though it appears 

 to be a renal response to a fall in blood volume; in this con- 



