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Immunization of female rats with crude preparations of delta 5-3 beta-hydroxysteroid dehydrogenase combined with complete Freund's adjuvant resulted in suppression of the endogenous enzyme activity in the ovarian interstitial tissue and the corpora lutea. As a result, estrous cyclicity, nidation, or maintenance of pregnancy was adversely affected in proportion to the level of the antibody to the enzyme following the series of immunizations. On the basis of the biologic response, it can be assumed that progesterone synthesis was reduced as a result of neutralization of enzyme action in the ovary by the formation of antibodies to the delta 5-3 beta-hydroxysteroid dehydrogenase. Further studies are required to verify this assumption.

Rhesus monkeys were immunized against the beta subunit of sheep luteinizing hormone (LH; oLHbeta) as an animal model for immunity against chorionic gonadotropin for fertility control. oLHbeta has been demonstrated to cross-react with rhesus chorionic gonadotropin (rhCG) but not rhesus LH. 13 multiparous monkeys received 50 mcg oLHbeta in complete Freund's reagent at 4 sc sites, repeated in 3 weeks and occasionally afterward. All developed circulating antibodies that bound hCG and oLH. RhCG was assayed in a competitive ligand binding assay using receptors from rat testis. Monkey antiserum bound hCG, 12.5% of which was displaced by 100 mcg rhLH. Antisera from 2 monkeys neutralized rhCG bioassayed in the immature rat uterine weight assay in a dose-related manner. After 2 immunizations 11 of the 13 macaques has regulat ovulatory menstrual cycles. 10 of them were mated 28 times, 1-5 each, at ovulation. There was only 1 pregnancy after 1 year in a monkey whose antibody titer had declined. In comparison, 5 of 10 controls, mated once each at ovulation, became pregnant. The mechanism by which immunization prevented pregnancy is unknown. Furthermore, use of a heterologous antigen in lieu of rhCG whose structure is unknown, may have minimized possible adverse effects.

Antisera to the conjugate of beta-human chorionic gonadotropin and tetanus toxoid (βhCG-TT) generated in rabbits receiving TT carrier preimmunization were characterized and compared with antisera from rabbits receiving the conjugate without preimmunization. Double immunodiffusion and immunoelectrophoresis were used to identify individual antisera components to the conjugate and its substructures. 125IhCG radioimmunoassay indicated similar antibody titers (P = 0.447) regardless of whether the rabbits were preimmunized with TT. However, bioneutralization of native hCG as measured by inhibition of prepubertal rat uterine weight increase was significantly more effective (P = 0.025) with antisera from rabbits which received carrier presensitization. These results demonstrate that carrier preimmunization provides a method for increasing the efficacy of neutralizing antibody produced against haptenic βhCG.