Evidence for an Osmoregulatory Role of Thyroid Hormones in the Freshwater Mozambique Tilapia Oreochromis mossambicus

The existing equivocal reports on the osmoregulatory role of triiodothyronine (T3) and thyroxine (T4) in teleosts prompted a reinvestigation of their osmoregulatory function in the euryhaline teleost Oreochromis mossambicus. Evidence is presented for thyroidal involvement in hydromineral balance in...

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Bibliographic Details
Published in:General and comparative endocrinology 2000-11, Vol.120 (2), p.157-167
Main Authors: Subash Peter, M.C., Lock, Robert A.C., Wendelaar Bonga, Sjoerd E.
Format: Article
Language:English
Subjects:
Animals
Brachial Artery
chloride cell
Chlorides - blood
Female
Immunohistochemistry - veterinary
ion transport
Male
Mozambique
Na+,K+-ATPase
Oreochromis mossambicus
osmoregulation
Sodium - blood
sodium pump
Sodium-Potassium-Exchanging ATPase - metabolism
teleost fish
thyroid hormones
Thyroid Hormones - physiology
Thyroxine - physiology
Tilapia - physiology
Triiodothyronine - physiology
Water-Electrolyte Balance - physiology
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Summary:The existing equivocal reports on the osmoregulatory role of triiodothyronine (T3) and thyroxine (T4) in teleosts prompted a reinvestigation of their osmoregulatory function in the euryhaline teleost Oreochromis mossambicus. Evidence is presented for thyroidal involvement in hydromineral balance in freshwater tilapia. Dose- and tissue-related responses to various T3 and T4 concentrations were observed in the branchial and renal tissues. The branchial Na+,K+-ATPase activity, known to reflect sodium pump dynamics, increased significantly after the administration of low doses of T3 (20 and 40 ng · g−1) or T4 (40 and 80 ng · g−1). Higher doses of T3 and T4 (>160 ng · g−1) did not change the enzyme activity, compared to sham-injected fish. Conversely, the specific activity of renal Na+,K+-ATPase decreased significantly at all doses of T3 or T4. Further, immunoreactive Na+,K+-ATPase in T4-treated fish increased in branchial chloride cells and this was coupled with a significant increase in the size of chloride cells. T4 treatment, however, did not change branchial chloride cell density. Plasma osmolality, [Na+], and [Cl−] increased, whereas [K+] decreased following low doses of T3 or T4. As expected, plasma levels of T3 and T4 increased significantly in a dose-dependent manner after a single injection of either T3 or T4. The basal levels of T3 and T4 were 4.45 ± 0.49 and 1.25 ± 0.26 nmol · L−1, respectively. This study shows that physiological concentrations of T3 (
ISSN:0016-6480
1095-6840
DOI:10.1006/gcen.2000.7542