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

Amniotic fluid beta-endorphin (beta-EP) and beta-lipotropin (beta-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 (L/S) 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) beta-EP (65.3 +/- 9.1 fmol/ml) and beta-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 beta-EP and beta-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 beta-EP and beta-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 beta-EP and beta-LPH concentrations of uncomplicated term pregnancies. In all patients but those with Rh-isoimmunization, beta-EP concentrations exhibited a positive correlation with beta-LPH levels. However, the molar beta-LPH:beta-EP ratio was significantly lower at term than during the early second trimester. Neither beta-EP nor beta-LPH correlated with the amniotic fluid L/S ratio and only beta-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 beta-EP is present in amniotic fluid and declines toward term. These data demonstrate that immunoassayable beta-LPH is present in amniotic fluid and show a more pronounced decrease toward the end of pregnancy than beta-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 beta-EP and beta-LPH and their possible role as markers of fetal response to stress remain to be elucidated.