Acetazolamide Pretreatment Restores The Blood Pressure-Lowering Effect Of Tempol In Female Spontaneously-Hypertensive Rats
Reneisha Sweet1, Noha M. Shawky2, Ruth M. Vinson2, Yvonne Zuchowski2, Edgar D. Torres Fernandez2, Jane F. Reckelhoff2
1Mississippi INBRE Research Scholar, Hinds Community College, Raymond, MS
2Department of Cell and Molecular Biology, Mississippi Center of Excellence in Perinatal Research, Women’s Health Research Center, University of Mississippi Medical Center, Jackson, MS
Oxidative stress is thought to be one of the mechanisms responsible for the regulation of blood pressure (BP). However, the role of oxidative stress in hypertension in females is controversial. Our lab has previously shown that Tempol (superoxide dismutase mimetic, antioxidant) failed to reduce BP in both adult and aged female spontaneously-hypertensive rats (SHR). Acetazolamide (AZT), a carbonic anhydrase inhibitor, inhibits Na+ reabsorption in the proximal tubules thus mediating an increased sodium reabsorption at the distal nephron, an effect that might promote distal oxidative stress. AZT was used in the current study to test the hypothesis that under conditions of distal oxidative stress, the BP-lowering effect of Tempol would be restored. Female SHR rats (9 months-old, n = 13) were implanted with radio-telemetry transmitters in the abdominal aortas and allowed 2 weeks to recover while placed in pairs. After recovery, rats were single-housed and cages were placed on receivers and blood pressure was recorded using Ponemah software (v6.3). BP was recorded for a baseline period (B) of 3 days, then the rats were given subcutaneous injections of AZT (100mg/kg/day) for a total of 27 days. After 16 days of starting AZT treatment, rats were divided into 2 groups; AZT (received regular drinking water, n = 6) and AZT + Tempol (received Tempol 30 mg/kg/d in drinking water, n = 7). Both groups continued to receive AZT injections daily. After 11 days of Tempol treatment, the rats were placed in metabolic cages for urine collection over 24 h. Urine samples were used for the estimation of urinary excretion of nitrates/nitrites (measure of systemic NO). Body weights were monitored twice a week and water intake was monitored daily to allow accurate determinations of the doses of administered drugs. MAP decreased gradually during the first 3 days of AZT treatment to comparable values in both groups (146 ± 3 in B to 135 ± 2 in AZT group vs 144 ± 3 in B to 133 ± 3 in AZT + Tempol group). Tempol treatment for 11 days caused 7 mmHg decrease in MAP compared to the MAP before starting Tempol (140 ± 1 to 138 ± 2 in AZT group vs 139 ± 2 to 132 ± 3 in AZT + Tempol group) which was significantly different compared to the baseline at days 3-11 of Tempol treatment (22-30 of the whole experiment). Additionally, Tempol caused a moderate increase in nitrate/nitrite levels (4.5 ± 1 in AZT vs 11.9 ± 4, n = 3-4, p = 0.08). Our data suggests that the blood pressure-lowering effects of antioxidants (Tempol) in females is dependent on renal sodium handling and distal oxidative stress.