Effect of Estrogen and Progesterone on Baroreflex Sensitivity in Acute Hypertensive Rats

Epidemiological studies suggested that incidence of cardiovascular diseases in menopause women is more than their nonmenopausal period. The cardioprotective role of estrogen may be responsible for some of these effects. In the present study we evaluated the role of female sex hormones on baroreflex sensitivity in acute hypertension state of rat. This was an experimental-interventional study that performed on 48 male and female rats. The male and female animals were separately divided into three groups included vehicle, estrogen and progesterone receiving groups (8 animals in each groups). Anesthetized female animals were ovariectomised, and then all animals were encapsulated with capsules containing sex hormones or solvent. 2 weeks after that, each femoral artery and vein cannulated under anesthetization to record mean arterial blood pressure (MAP), heart rate (HR) and also infusion of phenylephrin. ∆HR and ∆MAP were recorded before and after injection of phenylephrin, to evaluate the baroreceptors function, baroreflex sensitivity [BRS (∆HR/∆MAP)] index was used. The data obtained from power lab instrument and processed by computer. HR and MAP in estrogen and progestrone received groups, before phenylephrin injection (rest state), have no statistical differences with control group. BRS in the male estrogen-receiving group (0.6±0.03) was higher (p<0.05) compared to sham (0.48±0.05), also estrogen increased BRS (p<0.05) in female estrogen receiving group (0.76±0.03) compared to sham (0.45±0.05). Mean artrial pressure and heart rate in both estrogen receiving groups were reduced compared to vehicle group. Therefore it can be concluded that estrogen increased baroreflex sensitivity to prevent variation in acute blood pressure.