LONG-TERM OUABAIN ADMINISTRATION DOES NOT ALTER BLOOD-PRESSURE IN CONSCIOUS SPRAGUE-DAWLEY RATS

1. We tested the ability of ouabain to cause chronic hypertension by c ontinuously infusing ouabain for 28 days (mini-osmotic pump implantati on; i.p.), The blood pressure and metabolic effects of sham (150 mmol/ L NaCl; n = 12) or ouabain infusion (10 mu g/kg per day; n = 14; 100 m u g/kg per day; n = 14) were examined in conscious Sprague-Dawley rats . 2. Plasma ouabain concentrations measured after 28 days of ouabain i nfusion were as follows: sham, not detectable (n = 11); ouabain 10 mu g/kg per day, 0.60+/-0.07 nmol/L (n = 14); and ouabain 100 mu g/kg per day, 7.17+/-0.57 nmol/L (n = 14; P < 0.001). 3. Sham or ouabain infus ion did not alter food intake, bodyweight, water intake or urine outpu t in conscious rats. 4. Blood pressure was not altered by sham treatme nt. Ouabain at 10 mu g/kg per day or 100 mu g/kg per day did not produ ce consistent rises in blood pressure. Ouabain at 10 mu g/kg per day i ncreased blood pressure on treatment day 12 only (+ 6 mmHg; P < 0.05), while at 100 mu g/kg per day blood pressure increased on treatment da ys 16 (+ 9 mmHg; P < 0.05) and day 18 (+ 8 mmHg; P < 0.05) only. There was no significant difference in blood pressure between sham and ouab ain groups. 5. Renal blood flow was decreased in rats infused with oua bain at 10 mu g/kg per day (2.0+/-0.3 mL/min per 100 g bodyweight; n = 5; P < 0.01) and 100 mu g/kg per day (2.2+/-0.4 mL/min per 100 g body weight; n = 7; P < 0.05) compared with sham treatment (3.5+/-0.2 mL/mi n per 100 g bodyweight; n = 6), Renal vascular resistance was increase d in rats treated with ouabain at 10 mu g/kg per day (65.5+/-12.6 mmHg /mL per min per 100 g bodyweight; n = 5; P < 0.01) and 100 mu g/kg per day (66.0+/-15.6 mmHg/mL per min per 100 g bodyweight; n = 7; P < 0.0 5) compared with sham treatment (32.6+/-2.5 mmHg/mL per min per 100 g bodyweight; n = 6). 6. High plasma concentrations of ouabain do not ca use consistent increases in blood pressure in conscious Sprague-Dawley rats.