The ability of estradiol-17α to serve as a substrate for estrogen-2/4-hydroxylase in rabbit hypothalamic tissue was determined and compared to that of estradiol-17β. Both 2- and 4-hydroxy metabolites of estradiol-17α were formed by the hypothalamic tissue in vitro. The rates of formation of 2-hydroxyestradiol (2-OHE2)-17α and -17β were similar as were their kinetic constants (Km and Vmax). In addition, 2-OHE2-17α was shown to inhibit purified rat adrenal tyrosine hydroxylase with a potency comparable to that of 2-OHE2-17β, a finding similar to that reported by others with respect to catechol-O-methyltransferase. Since estradiol-17α has a markedly reduced affinity for estrogen receptors ccmpared with estradiol-17β, this steroid could be useful in studies designed to distinguish between receptor mediated effects of estrogens and effects that locally formed catechol estrogens may have through their direct interaction with catecholaminergic systems in neural tissue.
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