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Effects of bovine TSH on the tissue thyroxine level and metamorphosis in prometamorphic flounder larvae

1989; Elsevier BV; Volume: 74; Issue: 3 Linguagem: Inglês

10.1016/s0016-6480(89)80038-3

1095-6840

Yasuo Inui, Masatomo Tagawa, Satoshi Miwa, Tetsuya Hirano,

Physiological and biochemical adaptations

Bovine thyroid-stimulating hormone (TSH) was microinjected (0.2 μl/fish) into prometamorphic flounder larvae and the effects on metamorphosis as well as the tissue thyroxine (T4) and triiodothyronine (T3) levels were studied. After a single injection of TSH (5 mIU/g), the tissue T4 concentration increased markedly after 5 hr, reached a peak after 10 hr, and decreased subsequently. T4 concentration after 24 hr was still higher than in saline-injected fish but returned to the control level 48 hr after the injection. On the other hand, tissue T3 concentration was kept lower than the detectable level (0.2 ng/g) throughout the experimental period of 72 hr after a single injection of TSH (5 mIU/g). TSH treatment also accelerated the process of metamorphic climax, such as shortening of the second fin ray and eye migration. These results suggest that an increased secretion of TSH from the pituitary stimulates the thyroid, resulting in a surge of the tissue T4 concentration which induces the climax of the flounder larvae.