The immunocytochemical demonstration of human placental lactogenic hormone (hPL): a parameter for the functional capacity of the trophoblast.

Forty-two placentae from pregnancies of 36 to 42 weeks' gestation were examined: the maternal serum human placental lactogen (hPL) values of the mothers during the last week of gestation ranged between 3 and 12 micrograms/ml. hPL was demonstrated by the indirect immunofluorescence technique and was present in all placentae. A significant regional difference in hPL concentration was not found, but within individual sections focal differences in intensity were apparent. Of intensity group I (weakly positive) 92 per cent correlated with maternal serum hPL values of 3 to 6 micrograms/ml; 78 per cent of group II/III (very strongly positive) with values above 6 micrograms/ml. In the four-field Chi-square test the probability of error was at 5%. In 32 cases trophoblast islands (Islands of Ortmann) were present, of which 20 were hPL positive. Their degree of intensity corresponded to group I of the syncytiotrophoblast. Of the placentae showing hPL-positive Islands of Ortmann, 95 per cent correlated with maternal serum hPL values below 6 micrograms/ml whilst 70 per cent of the hPL-negative trophoblast islands correlated with serum values above 8 micrograms/ml. It is suggested that maternal serum hPL values are determined by the rate of synthesis of hPL by the placenta and not by the rate of secretion. The focal differences in intensity indicates that the serum level does not only depend on the absolute surface area of the trophoblast, but that there also exist qualitative and functional differences between different areas of the syncytiotrophoblast. Heterotopic hPL synthesis in the Islands of Ortmann is considered to be independent of hPL synthesis by the syncytiotrophoblast.