Key result
Estrogen supplementation significantly increased baroreflex sensitivity compared with control (p<0.01) in ovariectomized rats under acute hypertension.
Why the study?
Does estrogen enhance baroreflex sensitivity in ovariectomized rats under acute hypertension?
Does estrogen enhance baroreflex sensitivity in ovariectomized rats under acute hypertension?
Estrogen enhances baroreflex sensitivity under acute hypertension in ovariectomized rats, likely via the parasympathetic system in the NTS.
Hypothesis-generating for estrogen's baroreflex effects in this model; human studies needed before clinical consideration.
OBJECTIVE: To investigate the effect of estrogen exerted through the autonomic system in the nucleus tractus solitarii (NTS) on increasing the sensitivity of the baroreflex under conditions of acute hypertension in ovariectomized rats. METHODS: In this experimental study, conducted in Kerman University of Medical Sciences, Kerman, Iran from March 2010 to October 2010, 36 female rats were ovariectomized and then estrogen capsules were implanted beneath their skin. After 2 weeks, the left femoral vein and artery were cannulated for phenylephrine infusion and recording of mean arterial pressure and heart rate. Subsequently, atropine, propranolol, and saline were injected into the NTS, followed by measurements of changes in heart rate and changes in mean arterial pressure just prior to phenylephrine infusion. RESULTS: Estrogen increased the bradycardia response and inhibited the rise of mean arterial pressure; namely, after phenylephrine infusion, the change in heart rate was significantly lower in the estrogen-receiving group compared with the control group (p<0.05). Baroreflex sensitivity was significantly increased in the estrogen-receiving group compared with the control group (p<0.01). Baroreflex sensitivity was significantly attenuated in both groups (estrogen-receiving and control) after atropine injection, compared with after propranolol or saline injection (p<0.01). CONCLUSION: It is probable that under conditions of acute hypertension, estrogen affects the NTS through the parasympathetic system and enhances baroreflex sensitivity.
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Pourshanazari et al. (2013) studied acute hypertension (n=36). Estrogen vs. control was evaluated on baroreflex sensitivity (p=<0.01). Estrogen supplementation significantly increased baroreflex sensitivity compared with control (p<0.01) in ovariectomized rats under acute hypertension.
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