Effects Of Estrogen And Idoxifene On Cardiovascular System And The Underlying Mechanism

BackgroundIt is well known that estrogen played a protective role in cardiovascular system via genomic and non-genomic pathway, but the exact mechanism is far from clear.Despite the apparent beneficial effects of estrogen in preventing cardiovascular diseases, it was estimated that <10% of women who might benefit from this therapy are actually taking it, due to the side effects of estrogen. Recently some new drugs have attracted much attention, which differ from estrogen in a tissue specific manner. These kinds of drugs were named as selective estrogen receptor modulator (SERM). Idoxifene is a novel SERM.To date, the distribution of estrogen receptor (ER) in the hearts has not been investigated; The effects of estrogen on calcium homeostasis in cardiomyocytes are not illuminated, and its mechanism is not clear. The effects of idoxifene on blood vessel and ion channel of myocytes are also needed to explore. At present study, the immunohistochemistry, patch clamp, cell cultureand confocal microscope methods were used. Objective1. To examine the distribution of ERa in rat heart.2. To explore the effects of estradiol and idoxifene on calcium homeostasis of rat cardiomyocytes and its mechanism.;3. To investigate the effects of estradiol and idoxifene on ion channel of rat ventricular myocytes.4. To study the effects of estradiol and idoxifene on vessel and theirmechanism.. Results1. ERa was located in rat hearts and dominated in epicardium and endocardium, there was no difference in gender. The number of ERa positive cells decreased in ovarioectomized rats, The numbers (positive cell/HP) of ERa positive cells in epicardium and endocardium are listed as following respectively, normal group: 118145, 104138; ovariectomized group: 60+34, 56129 (P<0.05 vs control); estrogen replacement group: 107134, 99133(P>0.05 vs control). The cultured cardiomyocytes could also express ERa immuno-reactive positive substance, 17(3-estradiol (10" 8mol/L) enhance the staining, from 45.457?.954 in control group, to 62.87418.692 in ovariectemized group (P<0.001 vs control).2. 17-estradiol(l~30 umol/L) inhibited L-type calcium current in dose-dependently manner, the inhibitory effects of estrogen were not influenced by estrogen receptor blocker, ICI 182,780 (10 umol/L) and tamoxifenQO (omol/L). Extracellular perfusion of impermiant estradiol (100 umol/L) also had inhibitory effects on L-type calcium current, but intracellular perfusion did not affect L-type calcium current at same concentration.3. 17-estradiol(10 umol/L) increased intracellular calcium concentration ([Ca2+]i) of quiescent cultured cardiomyocytes of rat, but decreased calcium transient of cardiomyocytes with spontaneously contraction.4. 17-estradiol(l~30 jamol/L) inhibited L-type calcium current(ICa L) and outward transient potassium current (Ilo) of rat ventricular myocytes, idoxifene also inhibited ICa L, but had little effects on Ito.5. 17p-estradiol and idoxifene (10"9~10~5mol/L) relax superior mesenteric artery of rats in dose-dependently fashion, the effects were blocked by nitric oxide synthase inhibitor, L-NAME. Both 170-estradiol and idoxifene (10~9~10~5mol/L) increased nitric oxide production of cultured human endothelial cell line, E304, and they (10"5mol/L) also increased immunohistochemical staining of endothelial nitric oxide synthase in E304. Conclusion1. ERa immuno-reactive positive substance located in rat heart in specific pattern, ERa in the cardiomyocytes could be regulated by estrogen.2. 17p-estradiol affected calcium homeostasis by more than one pathway.3. l?p-estradiol inhibited L-type calcium channel via a stereo-specific receptor at plasma membrane.4. Idoxifene had different effects on ion channel of rat cardiomyocytes, in comparison with estradiol.5. Both 17p-estradiol and idoxifene relaxed the artery of rats, and the effects were involved in nitric oxide, both of them increased NO production via genomic and non-genomic pathway.