Manners of arginine vasopressin secretion in schizophrenic patients--with reference to the mechanism of water intoxication.

Water intoxication occurs almost exclusively in many patients with chronic psychiatric disorder. To elucidate the mechanism of this syndrome, we undertook the following animal experiments and clinical study. Twelve rabbits were given neuroleptics for eight weeks. From measurement of arginine vasopressin (AVP) secretion response to osmotic stimuli (fluid deprivation, partaking ad lib. and water loading), we found that chronic neuroleptic administration might raise the sensitivity of AVP escretion response. Then we investigated the manners of AVP secretion during ad lib. drinking in seventeen schizophrenic patients with hyponatremia and sixteen schizophrenic patients without hyponatremia. Normal range of plasma AVP was obtained from healthy volunteers by water loading. Only in both schizophrenic groups was plasma AVP detected below 270 mOsm/kg osmolality. We observed that sensitivity of AVP secretion response to osmolality was decreased in schizophrenic patients, regardless of the presence of hyponatremia. We hypothesize that the primary low sensitivity of AVP secretion response to osmo-receptor and the secondary renal hypersensitivity of AVP receptor may play the major role in the occurrence of water intoxication, linked to SIADH, in schizophrenic patients.