Introduction & Objective :Studies have shown that estrogen has important cardiovascular protective role. Nucleus tractus solitarii (NTS) is the termination point for all afferent of baroreceptor fibers that is important in regulation of heart function and circulation. For recognizing the estrogen mechanisms the role of estrogen through autonomic system in NTS have been evaluated. Hypertension state, estrogen increases baroreflex sensivity in NTS through autonomic system in rats.

Materials & Methods: Present study was an experimental-interventional study performed on 32 male rats. After introduction of anesthesia, ovariectomy and capsulation was happened. After two weeks their femoral artery and vein cannulated to recorded mean arterial blood pressure (MAP) and heart rate (HR), also for infusion of phenylephrin (as a vasoconstrictor). Then NTS by drugs (Propranolol, Atropin, Saline) have injected and ΔHR and ΔMAP recorded before & after injection of phenylephrin. For evaluating of baroreceptors sensivity, BRS index (Δ HR/Δ MAP) was employed.

Results: HR and MAP in estrogen received groups , without phenylephrine "rest state", had no significant statistical differences in comparison with control group. Estrogen in acute hypertension state "after injection of phenylephrine" enhanced reflex bradycardia and inhibited rising of MAP. ΔHR in estrogen received group was less than control group (p<0.05). ΔMAP in estrogen received group was significantly less than control group, (p<0.01). BRS in estrogen received group was significantly more than control group, (p<0.01). BRS in estrogen received group and control group decrease significantly after the micro-injection of Atropin compared with the microinjection of Saline or Propranolol in female rats.

Conclusion: The results demonstrate that estrogen enhanced bradicardial baroreflex sensitivity and decreased mean of arterial pressure. Micro-injection of Atropin decreased significantly BRS compared with Propranolol. Probably parasampatetic system is more invole in control of cardiovascular regulation in NTS and the Muscarin receptor in cardiovascular regulation is more important than beta-adrenergic receptor. It is concluded that estrogen in acute hypertension state in NTS is more effective through parasympatetic system on BRS and this can be useful in HRT/ERT even in male animals.