Estrogen metabolism in the equine conceptus and endometrium in early pregnancy

摘要

The equine conceptus produces significant quantities of estrogens, as early as day 12 (ovulation = 0) of gestation [1-3]. An increase in this activity occurs subsequently [3] and is reflected in the concentrations of estrogens seen in yolk-sac (ys) fluid [1]. We recently reported that the levels of estradiol-17#beta# (E2) in the ys fluid rise on day 14, two days earlier than for estrone (E1) and the sulfated forms of both estrogens [4]. Estrone sulfate (ELS) became the most abundant estrogen after day 16, but E2 remained higher than estradiol sulfate (E2S) after its initial rise. The exact role of estrogen production by the equine conceptus has not been determined, but some actions of estradiol may result from the formation of active estrogen metabolites, which function as local mediators in target tissues [5]. The local formation of hormonally inactive (or less active) estrogen conjugates is a further reason for the study.