Demonstration of a chorionic gonadotropin-like substance in rabbit morulae

Rabbit morulae were treated with specific indirect immunofluorescence and immunoperoxidase histochemical techniques. The first antibody in both systems was rabbit anti-human chorionic gonadotropin (hCG) beta-subunit. Negative controls revealed a complete absence of reaction. All morulae incubated with the double-antibody system showed a positive reaction. Rabbit morulae thus present a substance with antigenic determinants similar to the beta-subunit of hCG. The physiologic role of this substance is unknown.