The relationship of amniotic membrane 11-oxidoreductase activity to lung maturation in the human fetus

Abstract

This study demonstrates that the ability of amniotic membranes to interconvert cortisone and cortisol is significantly different in samples from pregnancies in which the infant develops respiratory distress syndrome (RDS) when compared with those from normal unaffected infants. We first calculated the percentage of conversion of cortisone to cortisol. The values were plotted according to gestational age, the control group and RDS group identified separately, and regression lines calculated. Comparison of the two regression lines showed them to be significantly different (P < 0.001). Comparison of expected values for all samples at a gestational age of 240 days again showed a highly significant difference (P < 0.001). After calculation of percentage of conversion of cortisol to cortisone, the regression lines for the two groups were shown to be not significantly different. However, after adjustment of data to a gestation period of 240 days the control group and the RDS group did show a difference (P < 0.01). For the “C-11 activation index,” a measure of the net gain or loss of biological activity at the C-11 position of the steroid molecule, direct comparison of regression lines failed to show a significant difference, but adjustment to 240 days of gestation showed the most significant difference seen between the two groups (P < 0.001). We also observed that when labor commences with spontaneous membrane rupture there is a significantly greater net production of cortisol by the membranes than if labor begins with contraction or bleeding (P< 0.001). The fetus, by extracting cortisol from the amniotic fluid, can maintain a significant part of his circulating plasma cortisol from sources other than maternal blood or the fetal adrenal. Our findings are compatible with the concept that the amniotic membranes are a major source of the free cortisol found in amniotic fluid. Although it seems that the membranes act as an extraadrenal source of cortisol for the fetus, they probably share a control mechanism with the fetal adrenal. Speculation: The appreciation of an extraadrenal source of glucocorticoids for the fetus may be only one example of a nonplacental origin for active compounds reaching the fetus, which may in the future be amenable for utilization or manipulation to the advantage of the preterm infant in utero. © 1978 International Pediatric Research Foundation, Inc.