Hyponatraemia is the most common electrolyte balance disorder occurring in hospitalized patients. The disease results frequently from inappropriate secretion of
vasopressin (
SIADH). It has been evidenced that the brain consequences of hyponatraemia are more dramatic in young females than in men or postmenopausal women. Since both
vasopressin and oestrogen have been reported to inhibit ion fluxes essential for the adaptation of the brain to the lowering of serum
sodium concentration, we sought to study the effect of acute and chronic hyponatraemia or hyponatraemia associated with
vasopressin on brain morphology in male and female rats. Hyponatraemia was induced with
vasopressin (AVP) or with
desmopressin (
dDAVP) in 12 male and 12 female adult Wistar rats for either 3 hours (acute) or 3.5 days (chronic). The brains of the animals with diagnosed hyponatraemia were fixed in 10%
formalin and, following the standard procedure, stained with haematoxylin and
eosin. Acute hyponatraemia resulted in white matter oedema with no obvious differences between genders or between groups with AVP- or
dDAVP-induced hyponatraemia. Although in chronic hyponatraemia most neurons and astrocytic nuclei appeared to be normal, some neurons were swollen or ischaemic ("dark" neurons) and astrocytes showed a weak reaction. The most spectacular differences between males and females were found in the appearance of blood vessels. Swollen endothelial cells were observed more frequently in female than in male brains and in AVP- than in
dDAVP-induced hyponatraemia. The widened Virchow-Robin spaces indicated perivascular oedema and blood-brain barrier damage. The results point to limited vascular adaptation to AVP-associated hyponatraemia in female gender.