| Summary: | v, 37 p. Much research has focused on understanding the relationship between thyroid function and reproduction, yet little knowledge has been obtained on exact mechanisms of interaction between these two systems in nonmammalian vertebrates. Although observed steroid effects are possibly modulated by influences on blood thyroid hormone transport proteins, information on thyroid hormone binding proteins in fish is severely limited. The effects of estradiol treatment on thyroid hormone transport in channel catfish (Ietalurus punctatus) and red drum (Seiaenops oeellata) were therefore examined to determine whether estrogen stimulation of vitellogenin, the yolk protein precursor, influences transport of thyroid hormones. Effects on availability of thyroid hormone for uptake into target cells due to estradiol-induced changes in blood plasma composition were examined by measuring free and total hormone levels in normal and estrogen-treated fish. Upon treatment with estradiol, vitellogenin production was stimulated in both species of fish, but total and free thyroid hormone levels were not affected by treatment. It was concluded that low doses of estradiol did result in vitellogenesis, but did not change levels of thyroid hormone. This conclusion contrasts with other studies using much higher doses of estradiol. Department of Biology. Texas A&M University. College Station, Texas.
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