Women exposed to cytotoxic chemotherapy are at risk of amenorrhea and premature ovarian failure due to the side effects of treatment. Few options are available to women who wish to preserve their germline, including embryo cryopreservation and ovary cryopreservation however these procedures are expensive, invasive, often requires delay of treatment and the presence of a partner. Most importantly all these options fail to protect ovarian function. Thus, there is a clear need to investigate an alternate strategy to protect the ovary from the cytotoxic effects so as to maintain oocyte quality as well as endogenous hormone production to support follicular growth and for maintenance of pregnancy. Recent studies in rodents have demonstrated that tamoxifen treatment prevented follicular loss and apoptosis from chemotherapeutic drugs and radiation-mediated injury. However, rodent models may not predict clinical outcomes. There is a need for a clinical model which would reflect clinical efficacy in humans. We evaluated the ovarian-sparing effect of tamoxifen on ovarian follicle reserve (primordial and primary follicles) of dogs. Ovarian cortical explant tissues from pre-pubertal dogs (N = 10) were collected at elective ovariohysterectomy and randomly assigned and treated for 72 hours with active metabolites of alkylating agent cyclophosphamide (4-hydroxycyclophosphamide; CTX) (0, 1, and 10 mM; C, CTXL, and CTXH) and tamoxifen (4-hydroxytamoxifen; TAM) (0 and 10 mM; C and TAM). Results presented as total normal follicle reserve based on histological morphology. High dose CTXH caused marked follicular loss (P < 0.05) whereas treatment with TAM decreased follicular loss (P < 0.05) from CTX in-vitro. TAM alone did not have an effect on morphologically normal reserve follicle counts (P > 0.05). This work also developed a dog ovarian cortical explant model to test efficacy and action of drugs in a model that share some genetic, physiological and environmental similarities with humans, have increased life spans and a propensity for tumors. Another goal of this study was to characterize anti-Mullerian hormone (AMH) in dogs with relation to puberty, age, numbers of reserve follicles, stage of estrus cycle and spay status to determine usefulness of AMH as an indicator of ovarian reserves and fertility in dogs. The data presented will show that spayed and intact female dogs can be successfully identified using a readily available human AMH ELISA. The results also demonstrated a significant negative relationship between AMH and advancing age and that there is a significant difference in serum AMH concentrations at anestrus and proestrus. Taken together, the results demonstrate that dog ovarian cortical explant culture system may be an alternative to test effects and actions of chemotherapeutic agents.
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