Effect of immunization with bovine luteinizing hormone receptor on ovarian function in cats

Abstract

Objective - To determine the effect of immunization with bovine luteinizing hormone receptor (LH-R) on ovarian function of cats. Animals - 9 adult female domestic cats. Procedure - 7 cats were immunized with 0.5 mg of LH-R encapsulated in a silastic subdermal implant (3 × 10 mm); 2 served as control cats. Receptors had 80% specific binding to 125I-human chorionic gonadotropin with a binding capacity of 2,682 pM/mg. Cats received booster injections of LH-R. Cats were induced to ovulate with luteinizing hormone (LH) releasing hormone on day 345. Samples of venous blood and vaginal cells were collected through day 395. Observation of estrus behavior continued until day 516. Serum concentrations of estradiol, progesterone, thyroid gland hormones, LH, and LH-R antibody were determined. Results - LH-R antibody was detected in the sera of immunized cats within 21 days after implantation. Detection of LH-R antibody was associated with suppression of serum progesterone to ≤ 0.5 ng/mL during the study period, compared with concentrations of 5 to 10 ng/mL in control cats. Immunized cats did not display signs of estrus. Release of LH after administration of LH-releasing hormone indicated an intact hypothalamic-pituitary axis but poor corpus luteum function. Serum estradiol concentrations remained between 30 to 40 pg/mL in immunized and control cats. With the decrease antibody titers, hormone concentrations returned to a pattern consistent with that during fertility. Conclusions and Clinical Relevance - Active immunization with LH-R suppressed corpus luteum function in cats. The effect was reversible. An LH-R-based antifertility vaccine may have clinical application in other vertebrates.