Estrogen Protects Vasomotor Functions in Rats During Catecholamine Stress

The incidence of dysfunctional vasomotor diseases has mostly occurred in postmenopausal women but not in premenopausal women. Hence, this study sought to investigate the impact of estrogen deficiency during catecholamine stress on vasomotor function. Also, attempts were made to utilize estrogen replacement therapy to mitigate the adverse effects (pathological remodeling) of stress on the aortic vessels to preserve vasomotor functions. To do this, female Sprague-Dawley (SD) rats were ovariectomized (OVX) along with sham operations (Sham). Day 14 after OVX operation, 17-estradiol (E₂) was subcutaneously implanted (OVX+E₂). Day 35 after operation, stress was induced by isoproterenol (ISO) subcutaneous injections. Clinically relevant blood pressure indexes (systolic, diastolic, and mean atrial blood pressures) were assessed in the rats. Aortic vascular ring tensions were assessed in vitro to ascertain the impact of E₂ on their vasomotor function. Aortic vascular rings (AVRs) from OVX+ISO exhibited a significant increase in contractility in response to phenylephrine than AVRs isolated from Sham+ISO rats. Also, sera levels of nitric oxide (NO) and endothelin-1 (ET-1) and the expression of p-eNOS/eNOS from vascular tissues were ascertained. We demonstrate that, during stress, E₂ prevented excessive weight gain and OVX rats had higher blood pressures than those in the Sham group. Further, we showed that E₂ decreases ET-1 expressions during stress while upregulating NO expressions via enhancing eNOS activities to facilitate vasomotor functions. Finally, histological assessment revealed the E₂ treatments during stress preserved vasomotor functions by preventing excessive intima-media thickening and collagen depositions in the aortic vascular walls.