Independent osmoregulatory control of central and systemic angiotensin II concentrations in dogs

In 14 dogs angiotensin (ANG II)-like immunoreactivity was analyzed in simultaneously collected samples of cerebrospinal fluid (CSF) from the anterior part of the third cerebral ventricle and of plasma. Plasma and CSF ANG II were not different in euhydrated conscious dogs (29.3 +/- 2.7 and 30.8 +/- 2.8 pg X ml-1, means +/- SE). During anesthesia CSF ANG II was not significantly altered, but plasma ANG II was more than doubled in comparison with conscious animals. In conscious dogs 24 h of dehydration with sodium-rich food significantly increased ANG II concentration in the plasma (to 59.8 +/- 16.5 pg X ml-1) and CSF (to 71.8 +/- 20.1 pg X ml-1). Subsequent rehydration by drinking caused no consistent changes in plasma ANG II within 90 min but reduced CSF ANG II significantly. Salt loading by infusion of 5% saline in seven conscious dogs produced a small but consistent decrease in plasma ANG II by 20%, on average, whereas CSF ANG II rose in five animals. The directions of changes in concentration of central ANG II compared with plasma ANG II suggest that central endogenous ANG II may function as a central osmoregulatory mediator independent from systemic ANG II.