Hydromineral and Metabolic Actions of Triiodothyronine during Hypoosmotic Challenge in Air-Breathing Fish (Anabas testudineus Bloch)
The effects of triiodothyronine (T3) on hydromineral and metabolic regulations were examined in the air-breathing fish Anabas testudineus, kept in either distilled water (DW) or freshwater (FW). Administration of T3 (40 ng g-1) for 24 h increased the plasma T3 level in both DW-challenged and FW fish. An activation of thyroid axis, as evident in the rise of plasma T4, occurred in DW-challenged fish after T3 injection whereas plasma T4 in FW fish classically declined. Substantial reductions in plasma glucose and plasma urea contents occurred after T3 administration in both FW and DW-challenged fish, and that indicates a metabolic role of T3 in hypoosmotic acclimation. An increased Na+, K+-ATPase activity occurred after T3 injection in the gills of FW fish, whereas the enzyme activity in the gills of DW-challenged fish failed to produce that effect. On the contrary, an increased Na+, K+-ATPase activity was found in the kidneys of DW-challenged fish but its activity failed to respond to T3 in FW fish. T3 administration had little effect on plasma Na+ and K+ contents in both FW and DW-challenged fish. Evidences are presented that thyroid has a direct role in hypoosmotic acclimation of climbing perch. Besides confirming the hydromineral and metabolic actions of T3, the sensitivity of thyroid axis to hyposmotic media has also been demonstrated in this air-breathing fish.
Fish, Thyroid Hormone, Metabolic Regulation, Na+, K+-ATPase Activity, Osmoregulation, Triiodothyronine.
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