
the effect of hydrochlorothiazide on water intake
and plasma osmolality in diabetes insipidus in
the rat
a fall in plasma osmolality accompanied the reduction of urine volume in
rats with hypothalamic diabetes insipidus, given hydrochlorothiazide and an
otherwise normal diet.  the plasma concentration was not reduced with a
high sodium intake, although urine volume still fell.  normal rats and hypo-
thalamic obese rats increased their water turnover after hydrochlorothiazide,
yet their plasma concentration fell.  moreover the antidiuretic response to
vasopressin, which is purely renal, was also accompanied by plasma dilution;
although it is self-evident that rats which drink less are less thirsty, the
reduction in thirst after hydrochlorothiazide may not be a direct result of the
change in plasma osmolality.
as previously shown in patients (kennedy and hill, 1963) a high sodium
intake increased free water clearance in diabetes insipidus but did not
interfere with the reduction of polyuria by hydrochlorothiazide, whereas a high
potassium intake reduced free water clearance and prevented any effect of the
drug on urine volume.
