Adenohypophyseal function in dogs with primary hypothyroidism and nonthyroidal illness.
BACKGROUND
A recent study of dogs with induced primary hypothyroidism (PH) demonstrated that thyroid hormone deficiency leads to loss of thyrotropin (TSH) hypersecretion, hypersomatotropism, hypoprolactinemia, and pituitary enlargement with large vacuolated "thyroid deficiency" cells that double-stained for growth hormone (GH) and TSH, indicative of transdifferentiation of somatotropes to thyrosomatropes.


OBJECTIVE
Similar functional changes in adenohypophyseal function occur in dogs with spontaneous PH as do in dogs with induced PH, but not in dogs with nonthyroidal illness (NTI).


METHODS
Fourteen dogs with spontaneous PH and 13 dogs with NTI.


METHODS
Adenohypophyseal function was investigated by combined intravenous administration of 4 hypophysiotropic releasing hormones (4RH test), followed by measurement of plasma concentrations of ACTH, GH, luteinizing hormone (LH), prolactin (PRL), and TSH. In the PH dogs this test was repeated after 4 and 12 weeks of thyroxine treatment.


RESULTS
In 6 PH dogs, the basal TSH concentration was within the reference range. In the PH dogs, the TSH concentrations did not increase with the 4RH test. However, TSH concentrations increased significantly in the NTI dogs. Basal and stimulated GH and PRL concentrations indicated reversible hypersomatotropism and hyperprolactinemia in the PH dogs, but not in the NTI dogs. Basal and stimulated LH and ACTH concentrations did not differ between groups.


CONCLUSIONS
Dogs with spontaneous PH hypersecrete GH but have little or no TSH hypersecretion. Development of hyperprolactinemia (and possible galactorrhea) in dogs with PH seems to occur only in sexually intact bitches. In this group of dogs with NTI, basal and stimulated plasma adenohypophyseal hormone concentrations were not altered.
Diaz-Espiñeira
M M
MM
Department of Clinical Sciences of Companion Animals, Utrecht University, The Netherlands.
Mol
J A
JA
Rijnberk
A
A
Kooistra
H S
HS
D000818:Animals; D004283:Dog Diseases / Q000378:metabolism*; D004285:Dogs; D007037:Hypothyroidism / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000502:physiology*