Perifused ovine placental tissue secretes beta-endorphin immunoreactivity

In vitro release of one of the pro-opiomelanocortin (POMC)-derived peptides, the endogenous opioid beta-endorphin (beta EP) has been examined in the sheep placenta by means of a perifusion system. Two zones of the cotyledon, the chorionic villus (highly vascularized fetal and maternal tissues in close apposition) and the maternal basal plate (or capsule), were examined in placenta at two stages of gestation--120 days (119.0 +/- 4.7, N = 4) and 140 days (143 +/- 1.8, N = 5) just before term. The chorionic villous tissue released more beta EP-like immunoreactivity (beta EP-IR) than did the basal plate tissue at both gestational ages. At 120 days' gestation the basal concentration of beta EP-IR released from the chorionic villus was 52 +/- 0.5 fmol mL-1 (n = 4), almost double the maternal basal plate tissue at 28.4 +/- 0.4 fmol mL-1 (n = 8). beta EP-IR secretory capacity increased significantly (P less than 0.05) with advancing gestational age. By Day 140, release had increased 3-4-fold to 181.8 +/- 0.8 fmol mL-1 (n = 16) in the chorionic villous tissue, and to a lesser extent in the basal plate tissue to 50.7 +/- 0.6 fmol mL-1 (n = 14). No stimulation of beta EP-IR secretion was observed in any tissue as a result of 30 min exposure to corticotrophin-releasing hormone (100 nmol L-1), a vital physiological secretagogue.(ABSTRACT TRUNCATED AT 250 WORDS)