Complementary antihypertensive action of rilmenidine on the pressure-natriuresis relationship and sodium preference in spontaneously hypertensive rats.

Previously, changes in position and slope of the pressure-natriuresis relationship have been used to characterize antihypertensive drugs in basic research. Rilmenidine may chronically reduce arterial pressure via central nervous system and renal imidazoline receptors. The present experiments were used to examine the shift in the pressure-natriuresis relationship during rilmenidine administration. We examined the effects of twice daily doses (1 and 3 mg/kg) for 6 days on the pressure-natriuresis relationship determined for control and treated spontaneously hypertensive rats (SHR) drinking tap water or 1% NaCl. The pressure-natriuresis relationship was shifted to the left for the 3 mg/kg dose and the slope was no different from the control. These experiments also indicated that rilmenidine might have an effect on sodium preference which was confirmed in a third series of experiments by permitting control and treated (3 mg/kg) SHR access to both tap water and 1% NaCl. This lack of change in slope indicates that, during rilmenidine treatment, the arterial pressure is relatively insensitive to sodium intake. The shift to the left indicates a restoration of the pressure-natriuresis relationship after chronic treatment with rilmenidine and a resetting of the long-term blood pressure control. Rilmenidine also reduces salt appetite in the SHR.