[Beta-endorphin-like immunoreactivity in peripheral blood, especially in erythrocytes during delivery].

Recently it was reported that beta-endorphin-like immunoreactivity (beta-ELI) was detectable not only in plasma, but also in erythrocytes. To assess the presence of beta-ELI in human erythrocytes and also to determine if erythrocyte-associated beta-ELI may be released into plasma in stress situations, beta-ELI concentrations in plasma and erythrocytes were measured in pairs in normal menstrual cyclic women, postmenopausal women and pregnant women during delivery. After separating from plasma, erythrocytes pellets were lysed by adding distilled water. Extraction of beta-ELI in plasma and RBC lysate was performed with a Sep-pack C18 cartridge (Waters Associates Inc.), and beta-ELI concentrations were measured with a New England Nuclear radioimmunoassay kit. The following results were obtained: 1) There certainly are two pools of beta-ELI; one in plasma, the other erythrocyte-associated. 2) During delivery beta-ELI concentrations in plasma showed a great change, but beta-ELI concentrations in erythrocytes remained almost unchanged. From these results it is unlikely that erythrocytes act as a peripheral reservoir of circulating beta-ELI.