Effects of immunization with human placental lactogen on reproduction in female rabbits

The effects on ovulation, implantation, and gestation were studied in rabbits actively immunized with crude or purified human placental lactogen (HPL). No effect on ovulation or implantation could be demonstrated in animals immunized with crude or purified HPL. Partial or complete fetal resorption and increased stillbirth rate were observed following immunization with the hormone. HPL-treated animals that were delivered of live pups failed to lactate. Ovarian and uterine weights of HPL-immunized rabbits (either puerperal or nonpregnant) were less than those of the respective controls. Activity of Δ53 ßol hydroxysteroid dehydrogenase in the ovaries was reduced in HPL-immunized rats that failed to breed compared to the nonpregnant control rabbits. These biological variations in immunized rabbits are assumed to be because of antibodies against injected antigen. The possible mechanism of these antibody actions is discussed.