Progesterone does not prevent ovariectomy induced NaCl-sensitivity in female spontaneously hypertensive rats.

Using a telemetry blood pressure monitoring system, we have reported that male spontaneously hypertensive rats (SHR) are NaCl-sensitive, manifesting significant increases in 24-hr MAP when exposed to high dietary NaCl, while female SHR and male and female Wistar-Kyoto rats (WKY) NaCl-resistant, manifesting no significant change in MAP when exposed to high dietary NaCl. In the current study, a radio-frequency pressure transducer (Data Sciences, St. Paul, MN) was implanted into the distal aorta of 10-wk female SHR and WKY, allowing for 24-hr blood pressure and heart rate monitoring (sample frequency every 4 min). At the time of instrumentation, the rats were either ovariectomized or left intact. Ten days later, ovariectomized rats were implanted with a subcutaneous slow-release progesterone (60 mg/pellet) or placebo pellet. Values at baseline on a normal (1%) and after 2 weeks of high (8%) NaCl diet were: Serum progesterone levels for SHR at the end of the 2-wk high dietary NaCl period were 7.1±2, 4.4±1, and 13.8±3 ng/ml for the intact, ovariectomy+placebo, and ovariectomy+progesterone SHR groups. These data demonstrate that ovariectomy significantly lowers baseline MAP while inducing NaCl-sensitivity in female SHR. Exogenous progesterone does not prevent the NaCl-sensitivity induced by ovariectomy.