Assessment of luteinizing hormone receptor expression in structural support tissues of canine hip and femorotibial joints

The association between gonadectomy and timing of gonadectomy, and the risk of canine cranial cruciate ligament disease: A systematic review and meta-analysis

OBJECTIVE

To determine if gonadectomy in dogs is associated with the risk of cranial cruciate ligament disease (CrCLD) and to quantify the magnitude of the association.

STUDY DESIGN

Systematic review and meta-analysis.

SAMPLE POPULATION

Comparative studies with gonadectomized and entire dogs, with CrCLD as an outcome measure.

METHODS

A systematic search of the primary and gray literature was performed. The effect size of the outcome measure was defined as the OR and 95% CI. Subgroup analysis was performed with sex, breed, and age at gonadectomy. A pooled OR (95% CI) was generated from meta-analysis of relevant studies. Certainty in the body of evidence was rated with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework.

RESULTS

The literature search yielded 1398 results and 24 relevant studies were included for synthesis. Gonadectomized female (pooled OR = 2.293, 95% CI = 1.768-2.945) and male (pooled OR = 2.117, 95% CI = 1.665-2.691) dogs were both at increased odds of developing CrCLD in comparison with entire female and male dogs, respectively. Subgroup analysis showed that gonadectomy at 1 year or less was consistently associated with an increase in odds of developing CrCLD in both sexes. Overall certainty in the evidence was rated as moderate. All included studies were observational and no controlled trials were available.

CONCLUSION

In data with moderate certainty, gonadectomy is associated with increased odds of developing CrCLD in both sexes, particularly in dogs gonadectomized at 1 year of age or less.

CLINICAL SIGNIFICANCE

This study provides an estimate of the true effect size of gonadectomy on the odds of developing CrCLD, which may be useful for clinical decision making surrounding gonadectomy and the timing of gonadectomy.

Understanding the effects of sustained supraphysiologic concentrations of luteinizing hormone in gonadectomized dogs: What we know and what we still need to learn

Removal of the gonads with surgical sterilization results in a loss of negative feedback to the hypothalamus and anterior pituitary. The sustained supraphysiologic luteinizing hormone (LH) concentrations in gonadectomized dogs can significantly alter organ function and even induce neoplastic changes. For example, gonad removal has a profound effect on thyroid function and is reported to be the most significant cause for the development of hypothyroidism in dogs. Thirty percent more gonadectomized dogs develop hypothyroidism compared with intact dogs. Within the canine thyroid, LH receptors are co-localized with thyroid stimulating hormone (TSH) receptors. Continuous LH receptor activation in gonadectomized dogs may interfere TSH receptor function by consuming second messengers involved in G-protein receptor cell signaling, preventing the action of TSH when it binds to its receptor in the thyroid, resulting in hypothyroidism. The incidence of anterior cruciate ligament ruptures is significantly increased following gonad removal independent of breed, sex, weight or body condition. Luteinizing hormone receptors are expressed in the cruciate ligament and continuous LH receptor activation may increase laxity in these ligaments, resulting in joint instability. Both male and female gonadectomized dogs are at a significantly increased risk for lymphoma and hemangiosarcoma. Luteinizing hormone receptors are also abundant in these tissues. Research in four canine hemangiosarcoma cell lines found that LH receptor activation induces cell proliferation. In addition, research in three canine T-cell lymphoma cell lines found that LH receptor activation induces cell proliferation, adhesion, and invasion as well as increases LH receptor expression. Research is needed to determine if LH reducing strategies using gonadotropin releasing hormone agonists will increase remission times in gonadectomized dogs with LH receptor-positive tumors. In conclusion, among the non-reproductive functions of gonads, suppression of LH secretion and resulting LH receptor overexpression appear necessary in maintaining endocrine, musculoskeletal, and anti-neoplastic health.

Canine splenic hemangiosarcoma cells express and activate luteinizing hormone receptors in vitro

OBJECTIVE

To determine luteinizing hormone receptor (LHR) expression and response to LHR activation in isolated canine splenic hemangiosarcoma cell lines in vitro.

SAMPLES

In vitro cultures of commercially available canine splenic hemangiosarcoma cell lines (EFS, GRACE-HSA, and DAL-4).

PROCEDURES

The percentage of each cell line expressing LHR was determined by immunocytochemistry. Cells were then treated with increasing doses (7.5 ng/mL, 75 ng/mL) of recombinant canine luteinizing hormone (cLH) for 48 hours and evaluated using a cell proliferation assay.

RESULTS

The percentage of cells expressing LHR was 17.2 ± 4.5%, 11.8 ± 3.1%, and 6.9 ± 2.5% in EFS, GRACE-HSA, and DAL-4, respectively. There was significant increase in cell count in the DAL-4 and EFS cell lines following a 48-hour incubation at the highest cLH concentration (P = .028 and P = .019, respectively). There was not a significant increase in cell count in the GRACE-HSA cell line at either cLH concentration.

CLINICAL RELEVANCE

Activation of LHR results in cell proliferation in some canine splenic hemangiosarcoma cell lines. These results may explain why spayed and castrated dogs with high circulating LH concentrations may develop hemangiosarcoma more frequently than intact dogs.