Roles of arginine vasopressin and atrial natriuretic peptide in polydipsia-hyponatremia of schizophrenic patients

Respective contributions of arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) to the urinary sodium concentration were evaluated in 23 naturalistic incidents of polydipsia-hyponatremia observed in 11 hospitalized schizophrenics (10 males and 1 female). The sodium concentration of the spontaneously excreted urine was examined before and after the forced water restriction. Before the water restriction, mean (+/-S.D.) plasma ANP was 52.8 +/- 33.9 pg/ml (range = 6.9-137). Plasma AVP levels were below 0.3 pg/ml in 15 episodes; relatively high levels (> or = 0.3) were noted in eight episodes. Means of urinary sodium concentration (mEq/l) were significantly higher in episodes with high AVP (> or = 0.3) alone (25.0 +/- 8.2, n=4), with high ANP (> 43) alone (21.3+/-7.4, n = 9), and with high AVP and ANP (26.8 +/- 6.4, n = 4) as compared to that of the low AVP (< 0.3) and ANP (< or = 43) group (13.5 +/- 3.7, n = 6). The data indicate that the elevated urinary sodium in polydipsic patients is possibly due to the AVP-induced antidiuresis and/or the ANP-induced natriuresis. In addition, we observed a close relationship between elevated plasma AVP and vomiting, suggesting that vomiting is one of the causal factors responsible for AVP elevations in this syndrome.