1. Urinary sodium excretion in anaesthetized rats subjected to high-sodium artificial cerebrospinal fluid (CSF) infusion into the lateral brain ventricle, was significantly higher than in rats infused with normal-sodium CSF.
2. Urinary immunoreactive 6-ketoprostaglandin F1α, the stable derivative of prostacyclin, was significantly reduced in the high-sodium CSF group, as compared with the normal-sodium CSF group.
3. When dog aortic endothelium was incubated in the presence of plasma, endothelial prostacyclin production was found to be inhibited by plasma from rats infused with high-sodium CSF compared with the effect of plasma from the rats infused with normal-sodium CSF.
4. Our results indicate that intracerebroventricular infusion of high-sodium CSF induces a natriuretic response and is associated with the appearance of a humoral factor which blocks prostacyclin byosynthesis.