The Effects of Ovariectomy and Estrogen Replacement Therapy on Blood Pressure and Renin-Angiotensin System in DeoxycorticosteroneAcetate-Salt Hypertensive Rat

Abstract

Background: Because the mechanisms responsible for postmenopausal hypertension are not fully understood, we evaluate the effect of ovariectomy (OVX) and estrogen replacement therapy on blood pressure (BP), plasma renin activity (PRA) in deoxycorticosterone acetate (DOCA)-salt hypertensive rat which is the typical model of low-renin, salt sensitive hypertension.

Methods: Sprague-Dawley rats at 7 to 8 weeks of age fed phytoestrogen-free chow and tap water for 5 days. Left nephrectomy was underwent at baseline except intact group. Six groups of female rats were studied: control group (n=6), OVX group (n=8), DOCA group (n=9), OVX+DOCA group (n=9), OVX+DOCA+E4 (17-beta estradiol replaced from 4 weeks after OVX) group (n=9), OVX+DCOA+E (17-beta estradiol replaced immediatedly after OVX) group (n=7). BP was measured by a tail-cuff method weekly. PRA was measured by radioimmunoassay at the end of animal experiments.

Results: Systolic BP of DOCA group at 9 and 12 weeks was significantly higher than those of other groups (all, p≤0.001). Systolic BPs of intact, OVX+DOCA+E4 and OVX+DOCA+E groups at 12 weeks were significantly lower than those of OVX, DOCA and OVX+DOCA groups (p<0.05, respectively). PRA of OVX+DOCA+E at 12 weeks was significantly higher than those of OVX, DOCA and OVX+DOCA (p<0.05, respectively).

Conclusions: The estrogen replacement after ovariectomy in DOCA salt hypertensive rat model significantly reduced blood pressure and increased PRA. These findings suggest that estrogen replacement in ovariectomized DOCA salt rat has a significant blood pressure lowering effect, which may be induced by inhibition of renin angiotensin system.