Nonpressor mechanisms in CNS-induced natriuresis.

Ventriculocisternal perfusion was performed in pentobarbital-anesthetized dogs. Perfusion of high Na (300 mM NaCl) artificial cerebrospinal fluid (CSF) (E) for 2 h was preceded by 2 h of control (C) and was followed by 2 h of recovery (R) during which normal (150 mM NaCl) artificial CSF was perfused. A time-control group was perfused with normal artificial CSF throughout C, E, and R. High sodium perfusion resulted in a marked natriuresis in each of nine animals and suppression of plasma renin activity. Theere were no simultaneous changes in mean arterial pressure, glomerular filtration rate, or renal plasma flow. Sodium excretion and plasma renin activity showed a slight gradual rise in the time-control group, but no significant differences were observed between the C and E periods; sodium excretion and plasma renin activity were similar in the high Na and time-control groups during C and R, but significantly different during E. It is concluded that when CSF sodium is elevated by perfusing artificial CSF, the resulting natriuresis and suppression of plasma renin activity are not caused by hemodynamic changes.