Hypernatraemia and Hyponatraemia 55 



presence of a water load, while the response to water depriva- 

 tion was nearly normal. Pitressin was not entirely without 

 effect on the urine flow since this diminished. 



The failure of Albert and Ivor to respond to pitressin might 

 represent the human counterpart of the experiments of 

 Wesson and co- workers (1950). Their dogs with an isotonic 

 expansion of the ECF did not respond to pitressin. 



We have mentioned that the failure of response was not a 

 complete one, and it therefore remains possible that the 

 original expansion of the ECF represented an effect of the 

 patients' own ADH, as Schwartz and co-workers (1957) 

 postulated for their two cases. Although Schwartz and co- 

 workers do not remark on it, there were occasions when their 

 patient W. A., like Albert, produced a hypotonic urine 

 following an additional expansion of the ECF. These observa- 

 tions would be consistent with the suggestion that when the 

 ECF is expanded beyond a certain point the kidneys become 

 refractory to the action of ADH. 



If we assume that an overproduction of ADH wasreponsible 

 for the hypotonicity of the ECF in Albert and Ivor, the 

 alternatives previously suggested still remain, whether the 

 stimulus to ADH production represented a homeostatic 

 mechanism for maintaining a hypotonic ECF in two people 

 who might have had "hypotonic" cells; or whether it repre- 

 sented a response to an abnormal stimulation of some un- 

 identified receptor. 



Summary 



The problem of hypernatraemia seems in general to be one 

 of water deficiency. That of hyponatraemia is sometimes 

 one of salt deficiency, but often one of excessive dilution of 

 the ECF with water. The latter seems to have been the fault 

 in the two patients we studied. Muscle biopsies revealed 

 normal or high sodium contents. In their responses to hyper- 

 tonic saline, water deprivation, and water loading their 

 homeostatic mechanisms were adjusted to maintain an 

 abnormally large volume of ECF with low tonicity. Though 



