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.