Renal excretory function in conscious Long Evans and vasopressin deficient (Brattleboro) rats after endothelin-A receptor inhibition

All experiments were performed on conscious, freely moving male Long Evans as well as Diabetes incipidus (Brattleboro) rats (300-320 g). The endothelin-A (ETA) receptor antagonist BQ-123 (Neosystem) was administered through femoral vein cannula. Arterial blood pressure was measured trough femoral artery catheter. The bladder was cannulated for urine collection via a small suprapubic incision. After a 40 min control period BQ-123 infusion (16.4 nmol/kg/min, 25 microliters/min) was started and continued for 50 min. The effect of 32.8 nmol/kg/min BQ-123 infused in conscious Brattleboro rats was also investigated. Plasma and urine concentrations of sodium, potassium and chloride as well as osmolality were determined. Glomerular filtration rate (GFR) was estimated using the clearance of endogenous creatinine. Endothelin-A receptor inhibition by 16.4 nmol/kg/min BQ-123 infusion in conscious Long-Evans rats decreased urine flow rate by 38.4% (p < 0.02) and increased urine osmolality by 30.3% (p < 0.05). Sodium, potassium, chloride excretion did not alter. Endothelin-A receptor inhibition by 16.4 nmol/kg/min and by 32.8 nmol/kg/min BQ-123 infusion in conscious Brattleboro rats did not produce any change in urine flow rate, urine osmolality or excretion of the electrolytes studied. Endothelins acting via ETA receptors may function as an inhibitor of water reabsorption in the kidneys of conscious rats.