CIRCADIAN-RHYTHM OF ARGININE-VASOPRESSIN IN HEPATORENAL-SYNDROME

The etiology of hepatorenal syndrome is still incompletely understood, but the nonosmotic release of arginine vasopressin (AVP) seems to hav e an important role. Since AVP presents a well-defined daily periodici ty in its production and secretion, the aim of the study was to invest igate the circadian rhythm in its circulating plasma concentrations in patients with hepatorenal syndrome, compared with healthy controls. V enous blood samples were drawn during a 24 hour period at 2 hourly int ervals from a peripheral vein in 10 healthy subjects and in 10 patient s with hepatorenal syndrome for the determination of the circulating p lasma levels of AVP by radioimmunoassay. Statistical analysis was carr ied out by the 'cosinor' method. The controls presented a significant (p < 0.002) circadian rhythm in the AVP circulating levels, whereas no rhythm (p > 0.05) was found in patients. The circadian rhythms were s ignificantly (p < 0.005) different between the two groups, patients ha ving higher mean daily concentration and lower circadian variation of AVP. These results confirm the existence of a well-defined circadian r hythm of AVP in healthy subjects, whereas the hepatorenal syndrome pat ients present a complete loss of the circadian rhythm. It could be hyp othesized that primitive damage in circadian time-keeping regulates th e circadian rhythm of vasopressinergic neurons, or has a secondary eff ect on the peripheral vasodilatation in the course of advanced liver d isease. This great upset in the temporal and functional organization, together with that of the renin-angiotensin-aldosterone system, could play an important role in promoting and/or in the maintenance of the h ydroelectrolyte imbalance that characterizes the hepatorenal syndrome.