Production and release of pregnancy - associated proteins by the human placenta perfused in vitvo

The human placenta produces a host of proteins which include human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) as well as the new generation of pregnancy-associated plasma proteins (PAPP’s) (Lin et al., 1974). We do not know the biological role of these PAPP’s and whether their synthesis is exclusively trophoblastic, or ectopic upon stimulation by pregnancy. The group is heterogeneous; M , values range from 21 600 (hPL) to 1 000 000 (pregnancy-associated plasma protein B, PAPP-B) and some members of the group are themselves heterogeneous in terms of electrophoretic mobility and M, (for a review see Bischof, 1984). While pregnancy-specific PI -glycoprotein (SP,) is now accepted to be of genuinely trophoblastic origin, pregnancy-associated plasma protein A (PAPP-A) and pregnancy-associated a2-glycoprotein (azPAC) have also been detected in the serum of non-pregnant women (Bischof et al., 1981; Bersinger & Klopper, 1984; Damber et ul., 1977). A perfusion system in vitro with separate perfusion of fetal and maternal compartment in an isolated lobe of placenta provides information on the placental synthesis and release of PAPP’s in the absence of maternal tissue. The aim of this study was to determine the rate of PAPP release as well as the net specific synthesis of hCG and the above-mentioned PAPP’s in the presence and absence of two protein synthesis inhibitors in the perfusing medium. A 2 6 5 0 g lobe of freshly delivered (spontaneously or by elective section) placenta was selected for perfusion. The chorionic vessels were cannulated for perfusion of the villous capillaries (fetal compartment). The maternal compartment was perfused with four to six fine needles introduced through the decidual surface into the intervillous space. This perfusion technique has been described before (Schneider P I al.. 1972). Both maternal and fetal circulations were first perfuscd for 1&15min in an open circuit and the venous return was discarded. Then the circuits were closed and the placenta was perfused with 120ml of buffer (33% Earle’s medium with mixed amino acids, 6.30 mg/ml; human serum albumin, 40 mg/ml; dextran 40000, 10 mg/ml; clamoxyl, 0.5 mgiml). Every 30 min a 5 ml aliquot was removed from both circuits and replaced with fresh medium. After 30min