Two estrogen replacement therapies differentially regulate expression of estrogen receptors alpha and beta in the hippocampus and cortex of ovariectomized rat

As estrogens have been implicated in altered cognitive function associated with menopause, the purpose of the present study was to determine the regulatory effects of different estrogen preparations on the expression of estrogen receptor subtypes in the hippocampus and cortex of ovariectomized rats. The expression of estrogen receptor mRNA and protein was determined with RT-PCR and immunohistochemistry, respectively. Two estrogen reagents, Premarin and Progynova, were used in the present study. Premarin, a conjugated equine estrogen, down-regulated ERα expression in the hippocampus and cortex of ovariectomized rats and had no effect on levels of ERβ expression in the same two regions. However, Progynova (valerate estradiol) was shown to up-regulate ERβ expression in the hippocampus and cortex and had no effect on the levels of ERα expression. Our present data suggest that different estrogen reagents used in estrogen replacement therapy could have different regulatory effects on the expression of estrogen receptor subtypes, which might, at least in part, explain why clinically, different estrogen preparations have distinct estrogenic effects on target organs.