Independence of the central nervous and the peripheral renin-angiotensin systems in the dog.

What regulates the activity of the central nervous renin-angiotensin system is not known. To define whether control of this central system is linked to that in the periphery, simultaneous blood and cerebrospinal fluid (CSF) samples for measurement of immunoreactive angiotensin II were drawn from anesthetized dogs during hemorrhage, furosemide-induced volume depletion, insulin-hypoglycemia, beta-adrenergic blockade and saline infusion. Despite vigorous increments or decrements in plasma innunoreactive angiotensin II, CSF levels remained stable. Since immunoreactive angiotensin II in dog CSF is claimed to be mainly the heptapeptide des-Asp1-angiotensin II (angiotensin III), the possibility that the level of this peptide within CSF simply reflects plasma concentrations was assessed by infusing angiotensin III (2.5 and 25 ng/kg/min intravenously, each for 60 minutes) and monitoring plasma and CSF peptide levels. Whereas plasma immunoreactive angiotensin II levels increased appropriately across the infusions, no change in CSF levels was observed. These studies indicate the angiotensin III does not cross the blood-CSF barrier, at least in the short term.