Ontogeny of pituitary beta-endorphin and related peptides in the human embryo and fetus.

In this study we evaluated the presence of proopiomelanocortin-related peptides (beta-lipotropin, beta-endorphin, and gamma-endorphin) in five embryos (5 to 10 weeks of pregnancy) and 11 fetal pituitaries (15 to 25 weeks) by means of high-performance liquid chromatography coupled with specific radioimmunoassays. Tissues were collected at laparotomy for ectopic pregnancy (five embryos) or after spontaneous (seven) or prostaglandin-induced (four) abortion. beta-Endorphin and beta-lipotropin were present starting at the seventh week of pregnancy while gamma-endorphin appeared only in the second trimester. During embryonic life opioid activity was limited to the cephalic portion. The three peptides, but little, if any, acetylated 1-31 beta-endorphin, were recognized in the fetal pituitary throughout the second trimester, at which time beta-lipotropin and beta-endorphin showed constant values in spite of increasing gamma-endorphin concentrations. beta-Lipotropin was the predominant peptide in both embryonic and fetal life. In conclusion, the three peptides related to proopiomelanocortin were expressed from the precursor at different times throughout development. By the beginning of the second trimester the pituitary processing of proopiomelanocortin is similar to that of adult life and the functional activity of the anterior lobe seems to prevail over that of the "fetus-related" neurointermediate lobe around the twenty-fifth week of pregnancy.