Immunohistochemical demonstration of luteinizing hormone-releasing factor-like material in human syncytiotrophoblast and trophoblastic tumours.

Luteinizing hormone-releasing factor (LRF)-like immunoreactivity was demonstrated by a three layer bridge immunoperoxidase technique in the syncytiotrophoblast of early human placenta, hydatidiform mole and choriocarcinoma. Anti-LRF antiserum was prepared by immunizing rabbits with synthetic LRF coupled to bovine serum albumin (BSA). The immunoreactive site of LRF reacting with the antiserum resided between residues Tyr(5) and Gly(10)-NH2. Syncytiotrophoblast cells of the normal placenta from the first half of pregnancy and trophoblastic tumours, showed staining with anti-LRF antiserum after solid phase immuno-adsorption with Sepharose-coupled BSA. Adjacent control sections showed no staining when prepared with anti-LRF antiserum after immunoadsorption with a Sepharose-coupled LRF-BSA conjugate. The findings of LRF-like material in the placenta prompted us to examine the effect of exogenous LRF on the circulating levels of placental proteins and protein hormones synthesized by the syncytiotrophoblast. Serum levels of chorionic gonadotrophin, pregnancy-specific beta-l-glycoprotein, placental protein five, and placental lactogen remain unaltered for 2 h after an intravenous bolus of LRF (100-300 micrograms) to ten pregnant volunteers admitted for legal abortion between 8 and 18 weeks of gestation. The significance of LRF-like material for the endocrinology of the normal and malignant trophoblast remains to be elucidated.