Dehydration and arginine vasotocin and angiotensin II in CSF and plasma of pekin ducks.

Osmolalities and, by radioimmunoassay, the contents of arginine vasotocin (AVT) and angiotensin II (ANG II) in simultaneously collected cisternal cerebrospinal fluid (CSF) and plasma samples were determined in chronically prepared conscious Pekin ducks (Anas platyrhynchos) adapted to either freshwater (FW ducks) or salt water (2% saline, SW ducks) for drinking. In FW ducks the AVT in CSF was approximately 10-fold higher than in plasma; ANG II concentration in CSF was about two-thirds of that in plasma. In SW ducks concentrations of AVT were increased approximately threefold and of ANG II fourfold in both CSF and plasma. Dehydration in FW ducks (24-48 h) increased AVT and ANG II in both CSF and plasma, the relative rise being greater in plasma. Within 150 min after rehydration plasma AVT fell at unchanged CSF AVT, whereas CSF ANG II fell at unchanged plasma ANG II. Hydration of SW ducks with freshwater had similar effects. The results indicate separate avenues of release of central and systemic AVT and ANG II and support the idea of an independent control of central ANG II as a mediator in osmoregulation, with CSF AVT reflecting the state of osmoregulatory activity of the hypothalamopituitary vasotocinergic system.