FRI384 Sterilization Of Female Dogs By A Neonatal Treatment Of Estrogen-Releasing Implants

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Abstract Disclosure: C. Park: None. P. Lin: None. S. Zhou: None. R.A. Hess: None. C. Ko: None. Hypothalamic Kisspeptin neurons that control the GnRH neuron activity are known to be a core regulator of the reproductive axis. Loss of the Kisspeptin-1 gene in these neurons results in infertility. Recent reports showed that inhibition of Kisspeptin neuron development by daily injection of 17β-estradiol benzoate (EB, 0.5 mg/day), a long-lasting estrogen, to neonatal female rats for 10 days causes sterility. We aim to develop a single injection solution for achieving sterilization in female dogs by targeting developing Kisspeptin neurons. In this study, we tested a working hypothesis that, in female dogs, extended exposure to EB for 2 weeks after birth by slow-releasing implants will result in sterility. This hypothesis was proposed based on our proof-of-concept study in which neonatal treatment of female rats with implants that contained 0.3 mg EB decreased the number of Kisspeptin neurons, and made them infertile permanently. To test the hypothesis in dogs, pellets that contained 0.5 mg (n=3) or 1.0 mg EB (n=2) and were designed to release EB for 2-3 weeks were subcutaneously implanted in female beagle dogs on postnatal day 6 (PND6). Intact dogs (n=4) were used as controls. The indices for female fertility (estrous cyclicity, ovulation) were assessed by daily vulva examination (swelling, discharge) and monthly measurement of serum progesterone levels. In addition, when a dog exhibited signs of estrus, the dog was bred with fertility-proven male dogs. During the 3 years of the study period, control dogs showed a minimum of 3 reproductive cycles (estrus, ovulation), and successfully produced puppies each time. Treated dogs displayed dose-dependent fertility outcomes; none of the EB 1.0 mg-treated dogs exhibited estrus nor had elevated serum progesterone levels, while two dogs out of the three EB 0.5 mg-treated dogs remained infertile. The other dog of the EB 0.5 mg group showed estrus signs during the study period and produced a litter when bred with a proven male. In the second experiment, implants that contained 0.5 mg (n=2) or 1.0 mg EB (n=3) were injected into female puppies on PND1. They are currently 1-1.2 years of age, and none have shown estrus/ovulation signs so far. Our study demonstrates that neonatal treatment of EB by slow-releasing implants sterilizes female beagle dogs. During the study period, the complete blood cell count and serum chemistry of treated dogs were within the normal range. This study shows that the non-surgical solution using EB implants is a promising approach to replace the current practice of sterilizing pets with surgical methods. Supported by NSF SBIR grant (#2052603) Presentation: Friday, June 16, 2023