Graduate Thesis Or Dissertation


Luteinizing Hormone Receptor Expression in Canine Lymphoma, Mastocytoma, and Hemangiosarcoma Public Deposited

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  • Luteinizing hormone (LH) stimulates the secretion of gonadal steroid hormones (testosterone in males and estrogen/progesterone in females) and is under negative feedback from gonadal hormones. In gonad-intact dogs, LH is secreted in low amplitude pulses of concentrations under 1 ng/mL; except for the day of the LH surge in females when the LH concentration rises between 1-2 ng/mL. However, in gonadectomized dogs, there is a loss of hormonal negative feedback, resulting in continuous supraphysiologic LH concentrations up to 20 times higher than measured for intact dogs. Although LH is mainly considered to be a reproductive hormone, there are dozens of non-reproductive tissues that contain LH/hCG receptors (LHCGRs). In dogs, gonadectomy increases the incidence of several non-reproductive long-term disorders including cancer. The purpose of this thesis research was to determine and demonstrate LHCGR expression in three canine cancers (lymphoma, mastocytoma, hemangiosarcoma). Additional research with hemangiosarcoma was conducted to examine the effect of LHCGR activation on cell count. It was hypothesized that LHCGR would be expressed in these tissues and that differences would exist between intact and gonadectomized dogs. In addition, it was hypothesized that LH/hCG receptor activation would induce cell proliferation. This thesis research found: 1) the increased risk of lymphoma in spayed and neutered dogs is not related to body weight, sex, immunophenotype, or tumor stage; 2) mastocytoma from gonadectomized dogs had a significantly higher percentage of LHCGR -positive mastocytoma cells compared to mastocytoma from intact dogs; and 3) there was a significant effect of LHCGR agonist (human chorionic gonadotropin (hCG) and canine luteinizing hormone (cLH)) exposure time on canine splenic hemangiosarcoma cell count. These results allow for a better understanding of the relationship between spaying or neutering and the development of cancer in dogs. The long-term goal of these experiments will be to provide support for a clinical trial to reduce circulating LH concentrations as an adjunctive treatment for these canine cancers.
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