Abstract
We examined the effect of estrogen on pressor responses to an α1-adrenoreceptor agonist (phenylephrine) in conscious female Wistar-Kyoto rats. At the age of 11 weeks, rats underwent ovariectomy or a sham procedure. At the age of 15 weeks, ovariectomized (OVX) rats received intramuscular injection of estradiol valerate (EV) 5μg (OVX+EV 5μg group; n =6), EV 25μg (OVX+EV 25μg group; n =7), or placebo (OVX group; n =8), and sham-operated rats received placebo (sham group; n =8). After 4 days, dose-pressor response curves to phenylephrine were examined under the condition where the renin-angiotensin, vasopressin and autonomic nervous systems were pharmacologically blocked. Ovariectomy shifted the dose-pressor response curve to phenylephrine leftward with a significantly decreased log ED50 (μg/kg) (the dose needed to reach 50% of the maximal response) (sham: 0.81±0.04; OVX: 0.57±0.05; p<0.05). Supplementation with EV 25μg, but not EV 5μg, reversed the dose-pressor response curve to phenylephrine in OVX rats to the level of the curve in sham-operated rats with a significantly increased log ED50 (μg/kg) (OVX+xEV 5 μg: 0.47±0.05; OVX+EV 25μg: 0.75±0.08). These results suggest that the physiological level of estrogen seen in intact female rats attenuates pressor responses to α 1-adrenoreceptor agonist, while supplementation with a moderate dose of estrogen is needed to restore such effects of physiological-level estrogen within a short-term period after chronic estrogen withdrawal. (Hypertens Res 2002; 25: 609-613)
