Dissociation of renin and aldosterone during dehydration: studies in a case of diabetes insipidus and adipsia.

The regulation of aldosterone was studied in a child with diabetes insipidus and adipsia, associated with holoprosencephaly. Plasma ADH was low and unresponsive to dehydration. Plasma renin concentration ranged from 52 to 1350 ng ml-1 h-1 at various degrees of hydration, and plasma aldosterone ranged from 4.7 to 104 ng/100 ml. Despite these wide ranges, the levels of the two hormones were not correlated. The aldosterone-renin ratio (log.) was inversely related to the plasma sodium concentration, while the plasma renin concentration (log.) was directly related to plasma sodium. Reduced values of both extracellular fluid volume (radiosulphate and sodium spaces) and total exchangeable sodium were measured when plasma sodium was elevated. Sodium depletion at the time when the patient was in a dehydrated state appeared to be caused, at least partly, by defective renal sodium conservation. Thus, in the dehydrated state, the patient showed the following unusual combination of abnormalities: hypernatraemia, sodium depletion, hyperreninaemia, and low to normal plasma aldosterone. The abnormal aldosterone-renin ratio was probably not caused by an intrinsic adrenal abnormality, since high levels of aldosterone were measured as long as a certain degree of hydration had been achieved with or without exogenous ADH, and since plasma cortisol was normal and responsive to exogenous ACTH. The results suggest that the responsiveness of the adrenal cortex to angiotensin may vary with extracellular sodium concentration. The direction of this effect, that is, suppression of aldosterone with increased sodium concentration, is not different from what is observed under experimental conditions, when extra-cellular sodium concentration is raised by infusions of hyperosmolar saline.