EFFECT OF RILMENIDINE ON ARTERIAL-PRESSURE AND URINARY OUTPUT IN THE SPONTANEOUSLY HYPERTENSIVE RAT

Rilmenidine is an antihypertensive agent acting at the imidazoline rec eptor that may have both central effects in the ventral lateral medull a and direct effects on the kidney to alter Na+ excretion. The present experiments examined whether rilmenidine induces a leftward shift or change in the slope of the pressure-natriuresis curve in the spontaneo usly hypertensive rat (SHR). A single oral gavage dose indicated that 3 and 10 mg/kg rilmenidine significantly lowers arterial pressure at 4 -12 h after administration by oral gavage. The effect of rilmenidine o n pressure-natriuresis was studied using twice daily doses of 1 and 3 mg/kg for control and treated SHR drinking tap water or 1% NaCl for 3 days. Na+ excretion was measured over 24 h, and mean arterial pressure was measured 6-8 h after the morning dose of rilmenidine. The results indicate that 1 mg/kg had no effect, while the pressure-natriuresis r elationship for the rats receiving the 3 mg/kg dose was shifted to the left and was not significantly different from the vertical slope of t he untreated SHR. This experiment also suggested that rilmenidine may attenuate the salt preference of the rats. This was confirmed in an ad ditional series of experiments in which the rats had access to both ta p water and 1% NaCl. Thus, rilmenidine shifts the pressure-natriuresis relationship to the left and reduces salt preference in SHR. (C) 1997 Elsevier Science B.V.