RENAL I-1-IMIDAZOLINE RECEPTOR-SELECTIVE COMPOUNDS MEDIATE NATRIURESIS IN THE RAT

In the present study, we investigated the renal actions of two compoun ds reported to interact with the imidazoline receptor: rilmenidine (I- 1-receptor selective, centrally acting antihypertensive) and agmatine (an endogenous clonidine-displacing substance). Rilmenidine (saline ve hicle, 3 or 30 nmol/kg/min) or agmatine (saline vehicle, 3 or 30 nmol/ kg/min) was infused directly into the renal artery of anesthetized (pe ntobarbitone) Sprague-Dawley rats (280-300 g) that had undergone a uni lateral nephrectomy 7 to 10 days before the experiment, Rilmenidine pr oduced an increase in urine flow rate at doses that failed to signific antly alter blood pressure, creatinine clearance, or heart rate. The i ncrease in urine flow rate was secondary to an increase in osmolar cle arance, primarily composed of sodium. Free water clearance was not alt ered at these infusion rates. Agmatine also increased urine flow rate at doses that failed to alter blood pressure, creatinine clearance, an d heart rate. The increase in urine flow rate was secondary to an incr ease in osmolar clearance, again primarily composed of sodium. The nat riuretic action of rilmenidine and agmatine, at doses that do not lowe r blood pressure acutely, could be beneficial in the antihypertensive actions of these centrally acting agents.