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Canine hemangiosarcoma expresses luteinizing hormone (LH) receptors
Throughout most of the developed world, surgical sterilization via gonadectomy has become a common tool for combating the overpopulation of unwanted dogs as well as to eliminate the risk of reproductive diseases in pet dogs. However, canine gonadectomy increases the risk of several non-reproductive long-term disorders possibly due to a loss in negative feedback to the anterior pituitary, which results in supraphysiologic circulating concentrations of LH. In addition to its reproductive hormone action, LH is a powerful mitogen in extragonadal tissues with LH receptors. Studies have confirmed the presence of LH receptors in vascular endothelial and smooth muscle cells in humans. Hemangiosarcoma is a rapidly growing, highly invasive cancer arising from the lining of blood vessels (mostly commonly the spleen in dogs). Gonadectomized (spayed) female dogs have two times the risk for developing hemangiosarcoma compared to unaltered females. We hypothesized that LH receptors would be present in vascular cells of canine hemangiosarcoma. The aim of study was to investigate if LH receptors were expressed in primary and metastatic lesions of canine splenic hemangiosarcoma using immunohistochemistry. Formalin-fixed surgical biopsies submitted to the Oregon State University Veterinary Diagnostic Laboratory were paraffin-embedded and sectioned (6 μm) onto charged slides. Testicular tissue from a separate dog obtained following castration was used as a positive control. All slides were deparaffinized, rehydrated, subjected to heat-induced epitope retrieval (#S1700, Dako). Endogenous peroxidase activity was inactivated with 3% H2O2 and nonspecific binding was blocked with 1% horse serum. Goat polyclonal anti-human LHR antibody (SC-26341, Santa Cruz Biotechnology) was applied at a 1:50 dilution. Negative controls from each tissue were treated in the same way except in absence of primary antibody. Slides were then reacted with biotinylated horse anti-goat IgG (Vector Laboratories, Burlingame, CA) and incubated with preformed avidin-biotin-peroxidase complex (#PK6105, ABC kit, Vector Laboratories) followed by Nova Red Peroxidase substrate (#SK4800, Vector Laboratories). Slides were counter-stained with hematoxylin, dehydrated, and mounted. Images were digitally captured at 400X magnification. LH receptor expression (cytoplasmic and granular) was found in splenic stromal cells of a primary tumor from one dog (identified by arrows on figure) but not in a primary splenic tumor or a mesenteric metastatic tumor from two other dogs. There was no positive staining in the negative sections. This is the first report shows that LH receptors are present in canine hemangiosarcoma and provides evidence for how gonadectomy may increase the incidence of cancer in dogs.
Keywords: Dog, Gonadectomy, Immunohistochemistry.