ABNORMAL HEMODYNAMICS AND ELEVATED ANGIOTENSIN-II PLASMA-LEVELS IN POLYDIPSIC PATIENTS ON REGULAR HEMODIALYSIS-TREATMENT

To investigate the cause and the mechanisms responsible of the compulsive thirst and excessive fluid intake observed in many patients on chronic dailysis treatment, we measured plasma antidiuretic hormone (ADH), angiotensin II (Ang II) and some hemodynamic parameters in seven polydipsic and in six normodipsic patients before hemodialysis, at the end of it and several times during the interdialytic interval. Before dialysis we found that ADH was elevated in both groups (6.9 +/- 1.9 vs. 6.9 +/- 1.3 pg/ml, respectively in polydipsics and controls), whereas Ang II was abnormally high only in polydipsics (51 +/- 12 vs. 11 +/- 3 pg/ml, P < 0.01); these patients also had significantly higher heart rate and cardiac indices and lower total peripheral resistances than control patients. Overall these hemodynamic indices were related with Ang II but not with ADH. Ang Il rose markedly in polydipsics after dialysis, reaching a peak at the fourth hour after its termination (136 +/- 12 pg/ml) and remained consistently elevated throughout the interdialytic period, whereas in controls Ang II was practically unchanged with respect to baseline. In contrast, ADH had minor and similar modifications in both groups, in whom also the hemodynamic changes were superimposable. Significant correlations were found between the absolute and percent changes of Ang II and those of plasma volume during the interdialytic interval (P < 0.001 for both), and between the individual values of Ang II measured during the whole study and the interdialytic weight gain (P < 0.05). These results demonstrate that polydipsic patients have abnormally high levels of Ang II before and after the hemodialysis-induced volume depletion. The high circulating levels of this peptide are expression of the hyperreactivity of the renin system that, apparently, represents the humoral counterpart of an hyperkinetic circulation which, in conjunction with the dipsogenic effect of Ang II, may be the cause of the compulsive thirst complained by these patients.