Active immunization of stumptailed macaque monkeys against luteinizing hormone releasing hormone, and its effects on menstrual cycles, ovarian steroids and positive feedback

Abstract

Five female stumptailed macaque monkeys with regular menstrual cycles were immunized against luteinizing hormone releasing hormone (LHRH) conjugated to tetanus toxoid. The conjugate was given in Freund's complete adjuvant (3 monkeys) or dipeptide adjuvant (2 monkeys). Only the 3 monkeys immunized using Freund's adjuvant produced LHRH antibody titres capable of having effects on menstrual cycles. Elevated levels of LHRH antibody were associated with an absence of preovulatory luteinizing hormone (LH) surges in serum and an inability to respond to an injection of oestradiol benzoate which produced an LH surge (positive feedback) in control animals. Cyclical rises in serum concentrations of follicle-stimulating hormone (FSH) were also abolished when LHRH antibody levels were elevated. These effects on LH and FSH caused a reduction in serum concentrations of 17β-oestradiol and absence of progesterone rises indicating inhibition of follicular development and ovulation, which resulted in amenorrhoea. Time to decline of LHRH antibody titres leading to re-establishment of menstrual cycles varied but could be reversed by booster immunizations.