Abstract
Simple SummarySpaying and neutering dogs is commonly used to prevent the birth of unwanted animals. However, spaying and neutering is associated with an increased risk of several long-term health problems including obesity, urinary incontinence, bladder stones, hypothyroidism, diabetes mellitus, hip dysplasia, cruciate ligament rupture, behavioral changes (including owner-directed aggression and fear), cognition problems, as well as several forms of cancer (including leukemia, prostate cancer, bone cancer, skin cancer, splenic cancer, and bladder cancer). An explanation of how spaying and neutering increases the risk of these long-term health problems is discussed in this review.Spaying and neutering dogs is commonly used to prevent the birth of unwanted animals and eliminate the risk of reproductive diseases. However, removal of the gonads prevents the feedback of estrogen and testosterone on the pituitary and hypothalamus. As a result, luteinizing hormone (LH) is continuously elevated at supraphysiologic concentrations. Although the main role of LH is for reproductive function (e.g., ovulation), there are LH receptors present in several normal tissues including the thyroid and adrenal glands, gastrointestinal tract, cranial cruciate ligament and round ligament, and lymphocytes. In addition, there are LH receptors present in several neoplastic tissues (e.g., lymphoma, hemangiosarcoma, mastocytoma, transitional cell carcinoma, and osteosarcoma). The role of LH receptors in non-reproductive normal and neoplastic tissues is not known but may stimulate nitric oxide release and induce cell division. The precise etiology of the increased incidence of several non-reproductive long-term health complications following spaying and neutering is not known but may be related to LH receptor activation in these non-reproductive target tissues. How these effects may be mediated is described in this review.
Highlights
Throughout most of the developed world, surgical sterilization has become a common tool for combatting the overpopulation of unwanted dogs and eliminating the risk of reproductive diseases in pet dogs [1,2,3,4,5,6]
Animals 2020, 10, 599 hormone (LH) stimulates the secretion of gonadal steroid hormones. These gonadal steroid hormones negatively feedback to the hypothalamus and anterior pituitary to decrease the secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH), respectively
It is possible that an increase in LH receptor activation in the cranial cruciate ligament results in increased laxity, which is responsible for the higher occurrence of ligament ruptures in spayed and neutered dogs
Summary
Throughout most of the developed world, surgical sterilization has become a common tool for combatting the overpopulation of unwanted dogs and eliminating the risk of reproductive diseases in pet dogs (e.g., mammary gland cancer and prostate hyperplasia/infection) [1,2,3,4,5,6]. In the normal adult mammal, the hypothalamus secretes gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary gland to release luteinizing hormone [8]. Animals 2020, 10, 599 hormone (LH) stimulates the secretion of gonadal steroid hormones (testosterone in males and estrogen/progesterone in females) These gonadal steroid hormones negatively feedback to the hypothalamus and anterior pituitary to decrease the secretion of GnRH and LH, respectively. With constant activation following gonad removal, these receptors can be upregulated (unpublished observations), further magnifying the effects of the supraphysiologic LH concentrations in non-reproductive tissues. The following review summarizes several non-reproductive long-term health complications resulting from spaying and neutering as well as discusses the possibility of how these effects are mediated by LH receptor activation in these non-reproductive target tissues
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