Estrogen receptors α and β -: Prevalence of estrogen receptor β mRNA in human vascular smooth muscle and transcriptional effects

Background-Estrogens have vascular effects through the activation of estrogen receptors (ERs). In addition to ER alpha, the first ER to be cloned, a second subtype called ER beta has recently been discovered. Methods and Results-Using a reverse-transcriptase polymerase chain reaction assay that employs the same primer pair to simultaneously amplify ER alpha and ER beta transcripts, we found that ER beta is the ER form that is predominantly expressed in human vascular smooth muscle, particularly in women. The transcriptional effects of the 2 ERs in transfected HeLa cells differed. In response to 17 beta-estradiol, ER alpha is a stronger transactivator than ER beta at low receptor concentrations. However, at higher receptor concentrations, ER alpha activity self-squelches, and ER beta is a stronger transactivator. Tamoxifen has partial agonist effects with ER alpha but not with ER beta. Conclusions-The protective effects of estrogens in the cardiovascular system of women may be due to the genomic effects of ER beta in vascular tissue.