Carcinoids

Gastrointestinal carcinoids are a heterogeneous group of tu­mors arising from the diffuse neuroendocrine system of the GI tract. In human patients, carcinoids have been reported to secrete a variety of regulatory substances such as histamine, serotonin, gastrin, somatostatin, tachykinins, peptide YY, pan­creatic polypeptide, calcitonin, CCK, motilin, and bombesin.

Human gastric carcinoids often secrete large amounts of his­tamine, which leads to a syndrome characterized by flushing, hypotension, lacrimation, cutaneous edema, and bronchocon­striction. In comparison, small intestinal carcinoids often se­crete serotonin and lead to flushing, diarrhea, and broncho­constriction.

Gastrointestinal carcinoids have been reported in dogs and cats.³⁴-³⁵ Recently, gastric carcinoids have been described in both a dog and a cat. Both patients were old and presented for chronic vomiting. The dog also showed weakness, ataxia, and coughing. It later deteriorated and was euthanized. The cat was surgically treated and remained free of clinical signs for 21 weeks, but then presented with clinical signs of chronic renal failure.

Signs of flushing, hypotension, or bronchoconstriction have not been reported in dogs or cats diagnosed with a GI carci­noid. This may reflect a lack of synthesis of these regulatory substances by canine and feline GI carcinoids, secretion of dif­ferent regulatory substances, or a relative resistance of dogs and cats to high plasma histamine and serotonin concentrations.

Careful evaluation of future cases, including the measurement of urinary histamine and serotonin metabolite excretion, im­munohistochemical behavior, and ultrastructural studies of the tumor cells, are required for a better understanding of this disease in dogs and cats.

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