Plasma levels of arginine vasopressin in hepatorenal syndrome.

BACKGROUND

The etiology of hepatorenal syndrome is still incompletely understood, but the non-osmotic release of arginine vasopressin (AVP) seems to have an important role in its pathogenesis. The aim of the study was to investigate the circulating plasma concentrations of AVP in patients with hepatorenal syndrome, compared with healthy controls, in relation with plasma osmolality.

METHODS

Venous blood samples were drawn in 20 healthy subjects and in 20 patients with HRS for the determination of the plasma levels of AVP by radio-immunoassay and of plasma osmolality. The comparison between the two groups was carried out by the Student "t"-test for unpaired data; the plasma AVP levels were correlated with the values of plasma osmolality by linear regression analysis.

RESULTS

The patients presented significantly (p < 0.001) higher plasma AVP levels in respect to controls; on the contrary, plasma osmolality was significantly lower in patients than in controls (p < 0.005). Whereas a significant (r = 0.83; p < 0.001) relationship was demonstrated between plasma AVP and osmolality in controls, no significant (r = 0.23; p > 0.05) correlation was found in patients.

CONCLUSIONS

These results confirm the existence of an activation in the release of AVP in hepatorenal syndrome, due to the activation of the sympathetic adrenal system and to hyponatriemia. The contraction of diuresis in hepatorenal syndrome, on the other hand, is not due to a deficiency in plasma AVP. AVP release occurs despite low plasma osmolality, which normally inhibits its secretion. This great upset in functional organization, together with that of the atriopeptin-renin-angiotensin-aldosterone system, could play an important role in promoting and/or in the maintenance of the hydro-electrolyte imbalance that characterizes the syndrome.