Some of the most reliable diagnostic tests in veterinary medicine are built on peptides. By injecting a precise hormonal signal and measuring how the body responds, veterinarians can probe the adrenal glands, thyroid, pituitary, and pancreas with a clarity few other tools offer. This is an educational overview of those stimulation tests.
The logic of a stimulation test
A peptide stimulation test works on a simple principle: give the gland its natural "go" signal, then measure the output. A healthy gland responds in a predictable range; a diseased one over-responds or under-responds. Because peptides deliver that signal cleanly and at tiny doses, they make ideal diagnostic probes.
ACTH and cosyntropin: the adrenal test
ACTH (corticotropin) and its synthetic analog cosyntropin (tetracosactide) stimulate the adrenal cortex to release cortisol. The ACTH stimulation test - a baseline cortisol sample, an injection of the peptide, and a second sample about an hour later - is a cornerstone of diagnosing adrenal disease in dogs, cats, and horses. It identifies both Cushing's disease (hyperadrenocorticism), common in dogs, and Addison's disease (hypoadrenocorticism), and it is used to monitor the response to Cushing's treatment. In newborn foals, cosyntropin stimulation reliably tests the hypothalamic-pituitary-adrenal axis. Cosyntropin is preferred when an animal reacts to the natural hormone.
TRH: thyroid and pituitary function
TRH (protirelin, thyrotropin-releasing hormone) stimulates the pituitary to release TSH, which then drives the thyroid to produce T3 and T4. Measuring that cascade helps diagnose thyroid disorders in dogs. In horses, a TRH stimulation test - alone or combined with a dexamethasone suppression test - is an important tool for diagnosing pituitary pars intermedia dysfunction (PPID), or equine Cushing's disease, one of the most common endocrine conditions in older horses.
Glucagon and C-peptide: the pancreas
Glucagon can be used as a diagnostic as well as a treatment. The glucagon stimulation test measures the insulin response after a glucagon injection; in a healthy dog insulin rises briefly, while a diabetic dog cannot mount that response. Rather than measuring insulin directly, clinicians often measure C-peptide, which is released alongside insulin and is unaffected by injected insulin - so it reveals how much insulin the animal's own pancreas is still making. A low C-peptide points to beta-cell loss; an abnormally high level can signal an insulin-secreting tumor.
Ceruletide and octreotide
Ceruletide (caerulein), an analog of cholecystokinin, stimulates bile flow and has been proposed as a liver-function test in dogs, particularly those with severe respiratory disease where liver involvement is a risk. Octreotide, a somatostatin analog, is used in a radiolabeled form to locate insulin-secreting pancreatic tumors by imaging, complementing the C-peptide picture.
Why this matters for research
These diagnostics show how exact and well-characterized peptide signaling is in living systems - the foundation on which newer peptide research is built. Researchers studying endocrine and metabolic models can explore our canine and feline research lines, supplied research-use-only with a COA on request. Further reading: the Merck Veterinary Manual and PubMed.
Frequently asked questions
What is an ACTH stimulation test in dogs?
A test that measures cortisol before and about an hour after injecting ACTH or cosyntropin, used to diagnose Cushing’s and Addison’s disease and to monitor treatment in dogs, cats, and horses.
How is equine Cushing’s disease diagnosed?
A TRH stimulation test, sometimes combined with a dexamethasone suppression test, is an important tool for diagnosing pituitary pars intermedia dysfunction (PPID), or equine Cushing’s disease, in older horses.
Why measure C-peptide instead of insulin?
C-peptide is released alongside the body’s own insulin and is unaffected by injected insulin, so it shows how much insulin the animal’s pancreas is still producing - useful in diabetic animals.
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External references: U.S. Food and Drug Administration · Peptide (Wikipedia)