[ role of estrogen on cardiovascular response due to GABA and glutamate receptors in Rostral ventromedial medulla in ovarictomized rats]

ABSTRACT

The Rostral Ventromedial Medulla [RVMM] is one of the nuclei controlling cardiovascular system. This study was performed to determine the effects of 17beta-estradiol [E], on the GABA and Glutamate cardiovascular responses of RVMM of female rats. Experiments were performed on 40 anaesthetized and paralyzed rats, divided into two groups of ovarictomized [OVX] and ovarictomized-estrogen treated [OVX+E] rats. Drugs [50 nl] bicuculline methiodide [BMI] an antagonist GABAA receptor [1 mM], phaclophen an antagonist GABAA receptor [5mM], and kynurenic acid a nonselective antagonist glutamate receptors [5 mM], were microinjected by micropipette into the RVMM using stereotaxic system. Blood pressure and heart rate were recorded before and throughout each experiment. The means of maximum changes of mean arterial pressure and heart rate were compared between groups of OVX and OVX+E and saline using ANOVA. In the OVX+E group, estrogen decreased the mean arterial blood pressure [P<0.05] and heart rate [P<0.001] compared to those of OVX group. Microinjection of BMI resulted in an increase of heart rate [HR] with no significant effect on the blood pressure [BP] in both OVX and OVX+E, but the increase of HR was significantly higher than in the OVX+E group [p<0.05]. Microinjection of phaclophen and kynurenic acid had no significant effect on HR and BP in either the OVX or the OVX+E group; not did microinjection of saline have any significant effects on HR and BP. The present data suggest that estrogen decreased the mean arterial blood pressure and heart rate, and in the RVMM of female rats augments the inhibitory effect of the GABAergic system on the heart rate via the GABAA receptors