Pituitary hormones in teleost fish with emphasis on gonadotropins

Ng, Tzi Bun (1979) Pituitary hormones in teleost fish with emphasis on gonadotropins. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This investigation on fish gonadotropins provides considerable evidence to support the concept of duality of gonadotropins in teleosts proposed by Campbell and Idler in 1976. Vitellogenic hormones were isolated from pituitaries of American plaice (Hippoglossoides platessoides) and winter flounder (PseudopTeuronectes americanus) and chum salmon (Oncorhynchus keta), devoid of oocyte maturational and androgenic activities, and they could be distinguished from the maturational hormones which were active in stimulating oocyte maturation and androgen production. The bioassays used to isolate the vitellogenic and maturational hormones utilized the hypophysectomized flounder as the assay animal, and this study represents one of the few investigations utilizing homologous bioassays to isolate fish gonadotropins. -- Vitellogenic and maturational hormones are different in their amino acid compositions, carbohydrate contents, immunological activities and chromatographic behavior on Concanavalin A-Sepharose. An antiserum to vitellogenic hormone was capable of inhibiting incorporation of vitellogenin into the ovary, whereas an antiserum to maturational hormone depressed the plasma concentrations of estradiol and vitellogenin, indicating that the two gonadotropins play different roles in fish reproduction. Chromatography of maturational hormone on Concanavalin A-Sepharose did not lead to isolation of additional material unadsorbed on the immobilized lectin. All available evidence thus suggest that the vitellogenic hormone and the maturational hormone are different entities. -- Thyroid stimulating hormone and gonadotropin were shown to be separate hormones. Two thyroid stimulating hormones could be isolated from pituitaries of both American plaice and winter flounder. The thyroid stimulating hormone unadsorbed on Concanavalin A-Sepharose stimulated mainly the production of triiodothyronine in hypophysectomized flounder while the thyroid stimulating hormone adsorbed on the immobilized lectin enhanced mainly the production of thyroxine.

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