Peer-reviewed veterinary case report
Pituitary changes in dogs after induced primary hypothyroidism over 3
By Diaz-Espiñeira, M M et al.·Published in Domestic animal endocrinology·2008·Department of Clinical Sciences of Companion Animals, Netherlands·View original on PubMed →
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Original publication title: Functional and morphological changes in the adenohypophysis of dogs with induced primary hypothyroidism: loss of TSH hypersecretion, hypersomatotropism, hypoprolactinemia, and pituitary enlargement with transdifferentiation.
- Species:
- dog
Plain-English summary
A group of seven beagle dogs developed primary hypothyroidism, which caused changes in their pituitary glands over three years. Initially, the dogs had high levels of thyroid-stimulating hormone (TSH), but these levels dropped over time, leading to an increase in growth hormone (GH) and a decrease in prolactin (PRL). The dogs' pituitary glands became enlarged, and some cells began to change in function. After starting treatment with l-thyroxine, the dogs showed improvements, with PRL levels normalizing and some pituitary functions returning to normal.
People also search for: dog hypothyroidism symptoms · beagle pituitary gland problems · l-thyroxine for dogs · dog growth hormone issues
Abstract
From case studies in humans it is known that primary hypothyroidism (PH) may be associated with morphological and functional changes of the pituitary. There is no insight into the time scale of these changes. In this study, seven beagle dogs were followed up for 3 years after the induction of primary hypothyroidism. Three of these dogs were followed up for another 1.5 years while receiving l-thyroxine. Adenohypophyseal function was investigated at 2-month intervals with the combined intravenous injection of CRH, GHRH, GnRH, and TRH, and measurement of the plasma concentrations of ACTH, GH, LH, PRL, and TSH. In addition, after 2 years of hypothyroidism a single TRH-stimulation test and a somatostatin test were performed, with measurements of the same pituitary hormones. Every 6 months the pituitary gland was visualized by computed tomography (CT). Induction of PH led to high plasma TSH concentrations for a few months, where after concentrations gradually declined to values no longer significantly different from pre-PH values. A blunted response to stimulation of TSH release preceded this decline. Basal plasma GH concentrations increased during PH and there was a paradoxical hyperresponsiveness to TRH stimulation. Basal GH concentrations remained elevated and returned only to low values during l-thyroxine treatment. Basal PRL concentrations decreased significantly during PH and normalized after several months of l-thyroxine treatment. The pituitary gland became enlarged in all dogs. Histomorphology and immunohistochemical studies in 4 dogs, after 3 years of PH, revealed thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and decreased numbers of mammotrophs. Several cells stained for both GH and TSH. In conclusion, with time PH led to a loss of the TSH response to low T4 concentrations, hypersecretion of GH, and hyposecretion of PRL. The enlarged pituitaries were characterized by thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and double-staining cells, which are indicative of transdifferentiation.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/18400449/