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Fifteen adult female baboons were immunized with a conjugate of tetanus toxoid coupled with a synthetic carboxy-terminal peptide of the beta-subunit of human chorionic gonadotropin and another 15 were immunized with tetanus toxoid. Freund's complete adjuvant was used in all immunizations. All females were placed with males of proven fertility during the third menstrual cycle after the primary immunization and those not sustaining pregnancy were mated in two additional consecutive cycles. Four pregnancies occurred following 42 matings in the conjugate-immunized group and 15 pregnancies resulted from 21 matings in the tetanus toxoid-immunized animals. Low levels of antibodies reactive to baboon chorionic gonadotropin were found in the pregnant animals in the conjugate-immunized group.

Baboons were immunized using a synthetic peptide adjuvant with two purified pig zona pellucida glycoproteins. The major zona pellucida glycoprotein (ZPI) was purified by preparative isoelectric focusing, and the 80 K deglycosylated zona pellucida protein (ZPIII) was purified by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis. The immunogenicity as well as the antigenicity of these proteins were evaluated by characterizing antibodies using the enzyme-linked immunoassay and by immunoblotting of zona pellucida proteins separated by high-resolution two-dimensional polyacrylamide gel electrophoresis. Both groups of animals developed antibodies that recognize the major zona pellucida glycoprotein, (ZPI) and immunoblotting procedures provide evidence that two of the major porcine zona pellucida glycoprotein families (ZPI and ZPIII) contain shared antigenic determinants. The animals immunized with ZPI showed decreased levels of estrogen throughout their menstrual cycles, and two of the animals ceased ovulation. All animals in the group immunized with ZPIII had a significant reduction in the numbers of antral follicles as compared with control animals. Although ovarian cyclicity was not altered significantly within a few months after immunization, two of the five animals in this group became amenorrheic by 8 months. Histologic analysis of ovarian tissue shows that follicles were absent or frequently abnormal in animals of both groups following long-term immunization. These studies demonstrate that the synthetic adjuvant is effective in inducing antibodies (to purified zona pellucida glycoproteins) that recognize antigenic determinants to either denatured or deglycosylated zona pellucida glycoproteins, and that some of these antibodies may interfere with normal ovarian function.

Immunization of female rabbits and mice with the sperm-specific isozyme of lactate dehydrogenase, LDH-C4, significantly reduced their fertility. Similar studies have been extended to nonhuman primates. Two female baboons, immunized with human LDH-C4, produced low antibody titers. These titers were markedly enhanced by booster injections of murine LDH-C4. An additional seven female baboons responded with relatively high antibody titers after receiving murine LDH-C4 as both priming and booster dosages. All nine females received injections of murine LDH-C4 at varying times determined by serum titer levels during fertility studies. These antisera reacted with human, mouse, and baboon LDH-C4. In a series of breeding experiments, 22 of 30 matings, or 73%, were infertile as compared with 28% in control matings. This contraceptive effect of the vaccine containing LDH-C4 was related to antibody titer and was reversible. Normal pregnancies ensued in animals in which the titer declined after termination of booster injections of vaccine.

Immune reactions to a number of hormones have been induced, but information is lacking on the feasibility of inducing immune reactions to homologous gonadotropins. Female rats immunized with diazotized and tyrosylated rat pituitary extract containing gonadotropic activity and emulsified in complete Freund's adjuvant expressed various reproductive disturbances such as increased cycle length (7.0 days), increased number of sterile matings, reduced implantation in animals becoming pregnant, and reduced ability to carry fetuses to term. These effects were not exhibited by rats immunized similarly with diazotized or tyrosylated rat pituitary extract containing no detectable gonadotropic activity. Rats not becoming pregnant had a significantly higher antibody level to rat luteinizing hormone than did rats becoming pregnant. No significant elevation of rat follicle-stimulating hormone antibodies was noted. It is concluded that auto-immune reactions to gonadotropins can be induced and that very low levels of antibodies have a significant effect on reproduction.

Implantation of pelleted agonistic analogs of luteinizing hormone-releasing hormone (LH-RH) into six pregnant baboons, ranging between 14 and 21 days after mating in individual animals, resulted in two abortions: one at 39 and the other at 67 days after mating. Plasma progesterone levels were low in treated animals through the 23rd day after mating, in spite of rising levels of plasma chorionic gonadotropin. Plasma levels of progesterone then rose rapidly to normal in five of six animals. Plasma estradiol levels were low from treatment on in the late-aborting animal but were normal until 5 days before delivery in the early abortant. The profile of circulating chorionic gonadotropin was truncated in treated animals, which may be the first indication of a paradoxical effect of LH-RH agonist on the trophoblast.