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Excessive Growth Hormone (Somatotropin) in Cats

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Acromegaly in Cats

 

Acromegaly is a rare syndrome resulting from the excessive production of the growth hormone somatotropin by tumors in the anterior pituitary gland of adult cats. Clinical signs of this syndrome are a result of the hormone's direct catabolic (breaking down) and indirect anabolic (building up) effects. 

 

The anabolic effects, meanwhile, are mediated by somatomedin C (insulin-like growth factor I), which is secreted by the liver in response to growth hormone stimulation. The excessive levels of somatomedin C, however, promote protein synthesis and growth in a variety of tissues such as the bone cartilage, soft tissues, especially in the head and neck region. Eventually these abnormalities in joint cartilage growth and metabolism alter normal joint biomechanics, which can lead to degenerative joint disease. 

 

Somatotropin also fights the action of insulin, which eventually causes pancreatic cell exhaustion and permanent diabetes mellitus.

 

Symptoms and Types

 

Initially, signs relate to unregulated diabetes mellitus. As the disease progresses, signs of heart failure, kidney failure, or central nervous system abnormalities caused by tumor expansion develop, including:

 

  • Increased appetite (polyphagia)
  • Excessive drinking (polydipsia)
  • Excessive urinating (polyuria)
  • Broadening of the facial features and lengthening of the lower jaw are common
  • Weight loss (initially), followed by weight gain due to increased bone and soft tissue mass
  • Systolic heart murmurs
  • Seizures and/or other central nervous system signs

 

Causes

 

The hypersecretion of the growth hormone somatotropin by an anterior pituitary tumor.

 

Diagnosis

 

You will need to give a thorough history of your cat’s health to your veterinarian, including the onset and nature of the symptoms. He or she will then perform a complete physical examination as well as a complete blood count, biochemistry profile, urinalysis, and electrolyte panel.

 

Other diagnostic exams include X-rays, echocardiogram, and CT (computed tomography) and MRI (magnetic resonance imaging) scans. CT and MRI scans are used to locate the pituitary mass. X-rays, meanwhile, often reveal an enlarged heart and sometimes fluid in the lungs, especially if left-sided congestive heart failure has already developed. And an echocardiogram will confirm heart abnormalities.

 

A radioimmunoassay for plasma somatomedin C is available at Michigan State University -- which can confirm the elevated plasma levels associated with acromegaly -- but this is often impractical.

 

 

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