Generation of estradiol within the pregnant guinea pig uterine compartment with special reference to the myometrium

Abstract

Between about 50 and 58 days of gestation, the guinea pig chorion becomes attached in its entirety to the uterine wall, suggesting a facilitation of transfer of agents such as steroids between these tissues. At a time between 59 and 64 days, relaxation of the pubic symphysis starts, and anywhere from 5 to 8 days after that event delivery takes place. The present in vitro study was undertaken to evaluate estrone sylfate as a substrate for local production of estradiol, via the action of estrogen sulfatase and 17-hydroxysteroid dehydrogenase, in chorion, endometrium and myometrium taken at four distinct stages of gestation, as follows: 50 days, representing pre-chorion attachment to the uterus (stage 50); 1 or 2 days before pubic symphasis relaxation (minus 1 day, or − 1 day), 1 day following relaxation (+1 day); and 1–2 days before delivery (late, or L). At these same stages, the metabolite patterns formed from estradiol were evaluated for endometrium and myometrium. Each of the tissues behaved somewhat differently. Overall hydrolysis of estrone sulfate by endometrium and myometrium exceeded that by chorion. Generation of free steroid from estrone sulfate increased 3-fold in chorion between stages 50 and −1 and during this period estradiol production from estrone sulfate increased 9-fold and continued to rise until delivery. Cytosolic estrogen sulfotransferase activity of chorion decreased 7-fold between stages 50 and −1. This suggested a tissue environment geared to producing potentially active estradiol. However, myometrium converted very little estrone into estradiol until just before delivery despite the facile formation of estrone from estradiol at stages −1, +1 and L. The control of estrogen metabolism by interaction of tissues in the uterus and by some form of enzyme regulation in these tissues suggests a possible role for locally produced estrogen in the stages leading up to parturition.