In ovine placenta, binucleate cells (BNCs) are formed from trophectodermal uninucleate cells and produce placental lactogen (PL) and pregnancy associated glycoproteins (PAGs). BNC numbers cells are stable throughout most of pregnancy, yet fall abruptly just before term (Wooding et al., 1994), at a time when endogenous fetal cortisol levels are rising. This study looked at the effect of abolishing the normal prepartum cortisol rise by fetal adrenalectomy on the BNC population in ovine placenta near term.
Under general anaesthesia between 115-117 days (d, term ~145d), 5 sheep fetuses were adrenalectomized (AX) as described previously (Fowden et al., 1993). Between 143-145d, cord blood samples and placentomes were collected from these animals and 8 further ewes with intact unoperated control fetuses (C). After fixation, BNCs were visualized immunohistochemically using antibodies specific for PL and PAGs as described previously (Ward et al., 2000). Mean ± S.E. values of BNC numbers per field of view (0.23mm2) and of fetal plasma cortisol concentrations measured by RIA are presented below for both groups.
Cortisol levels were significantly lower in AX (17.5±3.5 nanograms per millilitre; P<0.01) than C fetuses (82.6±8.2 nanograms per millilitre). BNC numbers were significantly higher in AX than C placentae using both PL (AX, 18±0.4; C, 11±1.5 P<0.01), and PAGs (AX, 16±0.9;C 9±1.4; P<0.02) antibodies. These findings show that AX prevents the normal prepartum decline in BNC numbers and suggest that cortisol may be responsible for this change.
Supported by the Avrith Research Studentship, Department of Physiology, University of Cambridge.
Fowden, A.L., Mijovic, J. and Silver, M. 1993. Journal of Endocrinology 137(2): 213-222.
Ward, J.W., Wooding, F.B.P., Forhead, A.J. and Fowden, A.L. 2000. Journal of Physiology 527: 56P.
Wooding, F.B., Morgan, G., Brandon, M.R. and Camous, S. 1994. Cell Tissue Research 276(2): 387-397.
03 - 04 Dec 2001
Society for Endocrinology