AJP - Renal Physiology, Vol 259, Issue 5 839-F846, Copyright © 1990 by American Physiological Society
Reduction of cerebral NaCl concentration can abolish mineralocorticoid escape
G. L. Pennington and M. J. McKinley
Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria, Australia.
The effect of lowering cerebrospinal fluid (CSF) Na concentration on renal
Na excretion (UNaV) was investigated in conscious sheep undergoing
mineralocorticoid escape induced by intravenous infusion of aldosterone (20
micrograms.ml-1.h-1) for 3 days. On the 3rd day of aldosterone
administration, when plasma and CSF Na concentration and mean arterial
blood pressure (MABP) were increased as a result of the mineralocorticoid
treatment, a reduction in the CSF Na concentration was induced by infusing
a Na-free solution of 300 mmol/l mannitol (1 ml/h) into a lateral cerebral
ventricle. This caused significant reductions in UNaV and MABP and a
significant increase in renal free water clearance (CH2O). There was no
significant change in glomerular filtration rate or plasma atrial
natriuretic peptide concentration, but renal lithium clearance decreased.
Simultaneous intravenous infusion of vasopressin (0.03 microgram/h) and
lowering of CSF Na concentration also caused significant reductions in UNaV
and MABP, but CH2O did not increase. We propose that increased Na
concentration of brain fluid may initiate natriuretic and pressor
mechanisms contributing to the process of mineralocorticoid escape. Reduced
UNaV may have been due to reduced MABP, but it is unlikely to have been due
to reduced plasma vasopressin levels.
