Amniotic fluid beta-endorphin and alpha-melanocyte--stimulating hormone immunoreactivity in normal and complicated pregnancies.

beta-Endorphin (beta-EP) and alpha-melanocyte--stimulating hormone (alpha-MSH) are members of a family of peptides which are found in the intermediate lobe of the fetal pituitary gland and placenta. In the present study, concentrations of immunoreactive beta-EP (i beta-EP) and alpha-MSH were determined by radioimmunoassay in the amniotic fluid compartment of both normal (n = 72) and complicated (n = 44) pregnancies. In normal pregnancies, there was a significant (p less than 0.05) fall in the mean amniotic fluid i beta-EP from the second to third trimester (from 175 to 132 pg/ml). A similar, but not statistically significant, decline in the mean amniotic fluid concentrations of alpha-MSH (from 46 to 34 pg/ml) was also noted. Concentrations of amniotic fluid i beta-EP showed a significant correlation with alpha-MSH (r = 0.61, p less than 0.001). Significant elevations of mean amniotic fluid i beta-EP but not alpha-MSH were found in pregnancies complicated by intrauterine growth retardation (215 pg/ml, p less than 0.001) and premature labor (225 pg/ml, p less than 0.001). Our findings suggest that levels of i beta-EP and alpha-MSH in amniotic fluid decrease from the second to the third trimester of pregnancy, and that elevation in i beta-EP concentration in amniotic fluid, in all probability, reflects the secretion of beta-EP by the fetus in response to fetal distress.