Vasopressin in blood and third ventricle CSF during dehydration, thirst, and hemorrhage

Samples of cerebrospinal fluid (CSF) were collected from the anterior part of the third cerebral ventricle of mongrel dogs with a chronically implanted device. Repeated experiments with simultaneous sampling of CSF and venous blood in 60- to 90-min intervals were performed in conscious dogs after 24-h water deprivation and during subsequent rehydration by drinking, during thirst stimulation by intravenous infusion of 5% saline, and during blood removal (12 ml.kg body wt-1). The CSF and plasma samples were analyzed for osmolality and arginine vasopressin (AVP) with a radioimmunoassay. Compared with normally hydrated dogs, 24-h water deprivation caused plasma AVP to rise significantly from 2.5 to 7.7 pg.ml-1 and CSF AVP from 24.2 to 31.3 pg.ml-1. Subsequent drinking significantly reduced plasma and CSF AVP. Thirst stimulation by hypertonic infusions was associated with rises of plasma and CSF AVP. Modest reduction of blood volume also increased both plasma and CSF AVP. Plasma AVP in each of the described physiological disturbances of salt or fluid balance was positively correlated with CSF AVP.