Testosterone Exacerbates Hypertension and Reduces Pressure-Natriuresis in Male Spontaneously Hypertensive Rats

Studies were performed in intact male and female, gonadectomized male and female, and gonadectomized female rats given testosterone for 5 weeks to investigate the role played by testosterone in altered blood pressure control and pressure-natriuresis in male SHR. Serum testosterone levels reached a peak at 12 weeks of age in intact male SHR. Systolic blood pressure, measured weekly from 5 to 20 weeks of age, was similar between groups until 12 weeks of age when blood pressure became higher in males (195+/-3 mm Hg) than in females (168+/-3 mm Hg) or males castrated at 4 weeks (173+/-4 mm Hg). At 17 to 19 weeks direct measurement of arterial pressure in anesthetized rats confirmed that mean arterial pressure was higher in male (182+/-1 mm Hg) than in female (159+/-2 mm Hg) and castrated male SHR (159+/-2 mm Hg). In addition, testosterone (5 mg in Silastic pellets, SC for 5 weeks) administered to ovariectomized (ovx+T) females caused arterial pressure to increase by mm 11% (175+/-2 mm Hg), which was significantly higher than in intact female, castrated male, or untreated ovariectomized (ovx) female SHR (158+/-2 mm Hg). Acute pressure-natriuresis was blunted in male SHR compared with females, castrated males, or ovx females, in which this relationship was similar. Pressure-natriuresis was also blunted in ovx+T females as found in intact male SHR. These data support the hypothesis that male sex hormones contribute to the exacerbation of hypertension in SHR by reducing pressure-natriuresis.