The changing estrogen content of the nuclear fraction of human myometrium during labor.

The cytosol and nuclear fractions were prepared from 32 pieces of myometrium obtained from 20 elective cesarean sections (regarded as typical of quiescent pregnancy (P)) and 12 emergency cesareans (performed after labor had started and therefore taken as typical of labor (L)). The nuclear fraction was purified by standard procedures. All protein-bound estrogen was released from the nuclear fractions, and the released estrogen simultaneously solubilized by denaturation with ethanol. The estriol (E3) and estradiol (E2) content of the alcohol solutions were assayed by radioimmunoassay with highly specific antisera for E3 and E2. In the L group, average E3 content was slightly (not significantly) lower, and average E2 content was significantly (P less than 0.005) higher, than in the P group. The E3/E2 ratio decreased dramatically (P less than 0.001) during this change from P to L.