Single neonatal estrogen implant sterilizes female animals by decreasing hypothalamic KISS1 expression

Abstract

Reproductive sterilization by surgical gonadectomy is strongly advocated to help manage animal populations, especially domesticated pets, and to prevent reproductive behaviors and diseases. This study explored the use of a single-injection method to induce sterility in female animals as an alternative to surgical ovariohysterectomy. The idea was based on our recent finding that repetitive daily injection of estrogen into neonatal rats disrupted hypothalamic expression of Kisspeptin (KISS1), the neuropeptide that triggers and regulates pulsatile secretion of GnRH. Neonatal female rats were dosed with estradiol benzoate (EB) either by daily injections for 11 days or by subcutaneous implantation of an EB-containing silicone capsule designed to release EB over 2–3 weeks. Rats treated by either method did not exhibit estrous cyclicity, were anovulatory, and became infertile. The EB-treated rats had fewer hypothalamic Kisspeptin neurons, but the GnRH-LH axis remained responsive to Kisspeptin stimulation. Because it would be desirable to use a biodegradable carrier that is also easier to handle, an injectable EB carrier was developed from PLGA microspheres to provide pharmacokinetics comparable to the EB-containing silicone capsule. A single neonatal injection of EB-microspheres at an equivalent dosage resulted in sterility in the female rat. In neonatal female Beagle dogs, implantation of an EB-containing silicone capsule also reduced ovarian follicle development and significantly inhibited KISS1 expression in the hypothalamus. None of the treatments produced any concerning health effects, other than infertility. Therefore, further development of this technology for sterilization in domestic female animals, such as dogs and cats is worthy of investigation.

Male animal sterilization: history, current practices, and potential methods for replacing castration

“…For example, in a recent study, newborn male rats injected daily with estradiol benzoate for 10 days, showed profound suppression of Kiss1 expression in the ARC region of the hypothalamus, and resulted in permanent inhibition of testicular growth and spermatogenesis ( 79 ). Similar research on females concluded that production of sterility was due to the precise targeting of the kisspeptin neurons during a critical period of neonatal development, which permanently suppressed pituitary gonadotrophins LH and FSH ( 57 ). Regardless of testicular effects, estrogen also has direct effects on the reproductive tract, particularly targeting the efferent ductules, where ESR has the highest expression and is co-expressed with AR ( 440 , 441 ).…”

“…Indeed, the removal or mutation of either Kiss1 or Kiss1r genes resulted in hypogonadism and sterility ( 73–78 ). Interestingly, studies revealed that exposure to estrogen during the neonatal period was shown to decrease the number of kisspeptin neurons present in the AVPV and ARC regions ( 57 , 79 , 80 ). The detailed mechanisms related to this phenomenon have not been fully elucidated, but some studies suggest that estrogen-induced apoptosis of kisspeptin neurons is a contributing factor ( 80 , 81 ).…”

“…In most cases, the results have not produced sterility, instead only contraception has produced (i.e., temporary inhibition of fertility). However, sterility can be produced by hormonal treatment, depending on the age at treatment ( 57 ). Congruently, immunocastration methods have been developed in the form of vaccines against specific peptide hormones and other proteins that are involved in the regulation of male reproduction.…”