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

Abstract

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 (≥0.3) were noted in eight episodes. Means of urinary sodium concentration (mEq/l) were significantly higher in episodes with high AVP (≥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 (≤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.