Effects of active immunization against oestradiol-17 beta, testosterone or progesterone on receptivity in the female rabbit and evaluation of specificity.

Juvenile does were actively immunized against oestradiol-17 beta, testosterone, progesterone or BSA. Depending on the antigen, the antibody titres at 17 weeks ranged between less than 1:10,000 and 1:500,000. Specificity of the antisera was high as judged by cross-reactivity studies. However, significant binding of [3H]oestradiol-17 beta (7-30%) was observed in 1:100 diluted sera raised against testosterone, and 21-48% binding of [3H]testosterone in sera raised against oestradiol-17 beta (binding in control animals being 1-8%). Total serum oestradiol-17 beta levels (RIA) were not only elevated (P less than or equal to 0.05, compared to controls) in does immunized with oestradiol-17 beta but also in does immunized with testosterone. Production of antibodies against progesterone did not interfere with receptivity but none of the does gave birth. Receptivity and consequently pregnancy were prevented by immunization against oestradiol-17 beta, suggesting that oestrogen is necessary for receptivity in the rabbit. Receptivity was also blocked in does immunized against testosterone. It is suggested that this is a non-specific effect and a consequence of oestradiol inactivation due to increased binding in serum.