β‐LIPOTROPHIN AND β‐ENDORPHIN PLASMA LEVELS DURING PREGNANCY

Abstract

.beta.-lipotropin (.beta.-LPH) and .beta.-endorphin (.beta.-EP) plasma levels were measured by radioimmunoassay in plasma samples from controls (10 healthy males and 26 young women in early follicular phase), from 82 pregnant women in weeks 9-40 after their last menstrual period, from 9 women just after delivery and the cord blood of their neonates, in 15 mixed cord blood samples and in 7 amniotic fluid samples obtained by amniocentesis. No sex differences were found in .beta.-LPH (120.6 .+-. 8.5 pg/ml) or .beta.-EP (31.1 .+-. 2.4 pg/ml) plasma levels or in their molar ratio (1.34 .+-. 0.09) (MR). .beta.-LPH plasma levels increased in early pregnancy (13-16 wk) (185.0 .+-. 27.1 pg/ml) and remained high until weeks 21-24, then declined to levels similar to those of controls. .beta.-EP plasma levels were significantly depressed in weeks 9-12 (20.7 .+-. 5.3 pg/ml), subsequently increasing to a maximum at weeks 36-37 (42.7 .+-. 6.8 pg/ml). .beta.-LPH/.beta.-EP molar ratio was about double normal in early pregnancy and decreased to normal in the 2nd half. .beta.-LPH and .beta.-EP present different patterns throughout pregnancy and .beta.-EP levels increase progressively, reaching the highest concentrations at term. At delivery, both .beta.-LPH and .beta.-EP showed maximum values (.beta.-LPH: 230.2 .+-. 20.4 pg/ml; .beta.-EP: 78.0 .+-. 7.4 pg/ml) and a MR of 1.02 .+-. 0.10 indicating that stressful situations, such as labor, stimulate a simultaneous rise in .beta.-LPH and .beta.-EP plasma levels. Cord blood specimens showed a wide range of values (.beta.-LPH:75-347 pg/ml; .beta.-EP:16-287 pg/ml) with a MR of 1.21 .+-. 0.14. Amniotic fluid samples obtained late in the 3rd trimester of pregnancy were characterized by .beta.-LPH levels of 119.4 .+-. 26.4 pg/ml and .beta.-EP levels of 29.6 .+-. 7.5 pg/ml.