Intracerebroventricular Infusion of Aldosterone Induces Hypertension in Rats*

There is suggestive evidence for the direct participation of mineralocorticoids in the production of centrally mediated hypertension. Unilaterally nephrectomized Sprague-Dawley rats received a continuous infusion for 30 days using implanted osmotic minipumps with 1) artificial spinal fluid (CSF) intracerebroventricularly (icvt); 2) 0.005 micrograms aldosterone/h icvt; 3) 0.005 micrograms aldosterone/h sc; 4) 0.5 micrograms aldosterone/h sc. There was no significant difference between the groups in average weight gain (52 +/- 2 g) or organ weight to body weight, nor was urine volume increased above normal except in the group receiving the high sc dose of aldosterone. Blood pressure was significantly elevated only in those animals receiving 0.005 micrograms aldosterone/h icvt and 0.5 micrograms aldosterone/h sc. A second experiment was done using a specific spironolactone-type mineralocorticoid antagonist, prorenone. The rats were grouped as follows: 1) CSF icvt; 2) 0.005 micrograms/h aldosterone icvt; 3) 0.005 micrograms/h aldosterone plus 0.005 micrograms/h prorenone icvt; 4) 0.005 micrograms/h aldosterone plus 0.02 micrograms/h prorenone icvt; 5) 0.02 micrograms/h prorenone icvt. This study confirmed that this minute dose of aldosterone infused icvt produced a statistically significant increase in blood pressure with no increase in urine volume. Both the low, 0.005 micrograms/h, and high, 0.02 micrograms/h, doses of prorenone antagonized the pressor effect of aldosterone when infused with aldosterone into the lateral cerebral ventricle. The groups receiving 0.02 micrograms/h prorenone icvt or CSF icvt did not differ significantly in those parameters measured. A dose of aldosterone that was too small to produce changes in blood pressure when infused systemically was found to produce hypertension without polydypsia/polyuria when infused intrathecally. This pressor effect could be blocked by the concomitant infusion of a specific antagonist, prorenone. The study presented offers strong circumstantial evidence supporting a direct hypertensinogenic effect of aldosterone within the central nervous system.