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Primary hypothyroidism in dogs is associated with elevated GH release
W M Lee1, M Diaz-Espineira, J A Mol
1Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 8, PO Box 80.154, NL-3508 TD Utrecht, The Netherlands.
The Journal of Endocrinology
|January 5, 2001
Summary
Primary hypothyroidism in dogs leads to increased basal growth hormone (GH) secretion and elevated insulin-like growth factor-I (IGF-I) levels. This endocrine shift causes physical changes that mimic acromegaly.
Area of Science:
- Veterinary Endocrinology
- Canine Physiology
- Hormone Secretion Dynamics
Background:
- Primary hypothyroidism in canines can induce physical changes resembling acromegaly.
- Growth hormone (GH) is secreted in a pulsatile manner, influenced by various physiological states.
Purpose of the Study:
- To investigate the impact of induced primary hypothyroidism on the pulsatile secretion patterns of GH in beagle bitches.
- To compare basal GH concentrations, GH pulse characteristics, and IGF-I levels between euthyroid and hypothyroid states.
Main Methods:
- Seven beagle bitches underwent surgical thyroidectomy and [(131)I]iodide treatment to induce hypothyroidism.
- Blood samples were collected every 10 minutes for 6 hours in both euthyroid and hypothyroid states.
- Plasma GH and IGF-I levels were quantified and analyzed for basal concentrations, pulse characteristics, and area under the curve (AUC).
Main Results:
- Hypothyroidism was associated with significantly higher basal plasma GH concentrations and mean GH AUC above zero.
- Mean GH AUC above baseline was significantly lower in hypothyroid dogs, indicating less GH secreted in pulses.
- Plasma IGF-I levels were significantly elevated in the hypothyroid state compared to the euthyroid state.
Conclusions:
- Primary hypothyroidism in dogs is characterized by elevated basal GH secretion and reduced pulsatile GH release.
- The observed hormonal changes, including elevated GH and IGF-I, contribute to physical manifestations mimicking acromegaly.
- Potential mechanisms include the absence of thyroid hormone response elements in the canine GH gene and altered supra-pituitary regulation.