Honors College Thesis
 

Luteinizing Hormone Receptor Expression in the Canine Coxofemoral and Femorotibial Joints

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  • Gonadectomy has been associated with a 1.5-2 fold increase in the occurrence of canine hip dysplasia and a 2-3 fold increase in the occurrence of canine anterior cruciate ligament (ACL) injury. In intact dogs, luteinizing hormone (LH) is secreted from the adenohypophysis to stimulate the synthesis of gonadal hormones, which negatively feedback to regulate LH secretion. Conversely, in gonadectomized dogs, no negative feedback occurs and LH concentrations are up to 20 times greater. LH receptors (LHR) are present in extra-gonadal tissues and their activation is associated with several long-term health conditions in dogs (e.g. urinary incontinence). Our objective was to use immunohistochemistry to determine if LHR were present in the structural support tissues of the coxofemoral joint, femoral head subchondral bone (FHSB) and round ligament (RL), and femorotibial joint, synovium and ACL. We hypothesized that LHR would be present and gonadectomy would increase LHR expression. Routine immunohistochemical techniques were utilized with goat polyclonal anti-human primary LHR antibody at a 1:50 dilution. LHR immunoexpression was detected using bright-field microscopy at 400X magnification in which bone marrow cells (FHSB) and synoviocytes (synovium) with visible nuclei were counted. For the RL and ACL, LHR immunoexpression in the fibrocytes was detected in a similar manner but quantified through a semi-quantitative approach with the product of scores for positive staining percentage and staining intensity. Although expression varied, all tissue types studied showed positive LHR expression. In the RL, spayed females had significantly greater LHR expression in fibrocytes compared to neutered males (4.33±2.89 vs. 0, p=0.03). Additionally, all females studied had significantly greater LHR expression in fibrocytes compared to all males studied (4.75±2.5 vs. 0, respectively; p=0.004). There was no significant difference between sex or gonadal status in the FHSB, ACL, or synovium tissues studied. The etiopathogenesis for the increased incidence of hip dysplasia and ACL injury in gonadectomized dogs remains unknown, but the presence of LHR in combination with increased plasma levels of LH suggests that persistent LHR activation in these structural support tissues may play a role. LHR activation is known to stimulate nitric oxide release and remodeling processes, which in predisposed breeds could result in the laxity associated with the pathophysiology of these musculoskeletal diseases. Key Words: Luteinizing hormone, luteinizing hormone receptors, canine hip dysplasia, canine ACL injury, gonadectomy
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  • Dr. Howard Meyer and the OSU Agricultural Research Foundation
  • The DeLoach Work Scholarship from the OSU Honors College
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  • 2018-06-06 to 2019-07-12

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