Amniotic fluid β-endorphin and β-lipotropin concentrations during the second and third trimesters

Abstract

Amniotic fluid β-endorphin (β-EP) and β-lipotropin (β-LPH) were measured by radioimmunoassay after silicic acid extraction and gel chromatographic separation of the two peptides in uncomplicated second-trimester and term pregnancies, in diabetic patients at term, and in pregnancies complicated by Rh-isoimmunization, premature labor, and intrauterine growth retardation. Furthermore, the lecithin/sphingomyelin (LS) ratios as well as the dehydroepiandrosterone sulfate (DHEA-S) and cortisol levels were determined in most of the amniotic fluid specimens. Both the mean (±SE) β-EP (65.3 ± 9.1 fmol/ml) and β-LPH (150 ± 15.8 fmol/ml) concentrations were significantly higher in the 20 patients with normal pregnancies of 16 to 21 weeks' duration than those found in 21 patients with uncomplicated term pregnancies of 38 weeks' gestation, averaging 42.6 ± 6.0 and 80.1 ± 10.7 fmol/ml, respectively. The mean amniotic fluid β-EP and β-LPH concentrations measured in the latter subjects were similar to those observed in 23 diabetic patients with otherwise uncomplicated term pregnancies. The mean amniotic fluid β-EP and β-LPH levels found in the limited number of patients with Rh-isoimmunization (N = 9), premature labor (n = 8), and intrauterine growth retardation (n = 5) with pregnancies of 24 to 36, 24 to 36, and 34 to 38 weeks' gestation, respectively, were not significantly different from the mean amniotic fluid β-EP and β-LPH concentrations of uncomplicated term pregnancies. In all patients but those with Rh-isoimmunization, β-EP concentrations exhibited a positive correlation with β-LPH levels. However, the molar β-LPH: β-EP ratio was significantly lower at term than during the early second trimester. Neither β-EP nor β-LPH correlated with the amniotic fluid LS ratio and only β-LPH exhibited a significant inverse correlation with amniotic fluid DHEA-S. The latter was significantly higher in uncomplicated term than second-trimester pregnancies. These results confirm that immunoassayable β-EP is present in amniotic fluid and declines toward term. These data demonstrate that immunoassayable β-LPH is present in amniotic fluid and show a more pronounced decrease toward the end of pregnancy than β-EP. Neither peptide, at least on account of the amniotic fluid levels, appears to be associated with fetal maturation. The physiologic significance of amniotic fluid β-EP and β-LPH and their possible role as markers of fetal response to stress remain to be elucidated.