Morphometric analysis of gap junction density in human myometrium at term.

In the human myometrium, the formation of gap junctions in the various stages of labor and, in correlation with the concentration of progesterone in the maternal blood, has not been described adequately. The accepted hypothesis that raised concentrations of progesterone in maternal blood in animals prevent the formation of gap junctions was scrutinized in human myometrium. Myometrial tissue was examined by electron microscopy for the presence of gap junctions and analyzed morphometrically in 17 women who had an elective or emergency cesarean operation at the 38th or 39th week of pregnancy. The concentrations of progesterone and estradiol in the maternal and cord blood was measured by means of radioimmunoassay. The frequency and area of gap junctions varied in relation to the presence or absence of labor. In the myometrium of women in labor, gap junctions were most frequent (5.2/1000 microns of cell membrane), their area largest (0.32 microns 2/1000 microns of cell membrane) and their fractional area greatest (0.20%). When the women were not in genuine labor or when contractions were weak, the percentage fractional areas of gap junctions were low (0.020-0.090) and the gap junctions very small. In the pre- and active phases of labor, the concentration of progesterone in maternal blood was significantly higher (p < 0.025 and 0.03 respectively) than in women who were not in labor. Hence, despite high concentrations of progesterone in the maternal and cord blood at term, the myometrium presented numerous gap junctions of relatively large area.