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Search for other papers by M Sakai in
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Search for other papers by H Kawauchi in
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Abstract
The activation of rainbow trout (Oncorhynchus mykiss) phagocytic cells by chum salmon GH, prolactin (PRL) and somatolactin (SL) was investigated in vitro. Rainbow trout kidney leucocytes were cultured in RPMI 1640 medium containing 1, 10, 50 or 100 ng of each hormone/ml and the production of superoxide anion was measured using reduction of nitroblue tetrazolium (NBT) and ferricytochrome C. Macrophages incubated with 10–100 ng GH or PRL/ml showed significantly enhanced production of superoxide anion in both the NBT and ferricytochrome C tests compared with control macrophages (without hormone). SL did not induce enhanced production of superoxide anion in macrophages. The phagocytic cells treated with GH or PRL also showed increased phagocytic activity and phagocytic index. However, the cells treated with SL showed no enhancement of phagocytic activity or index. These results indicate that GH and PRL stimulate macrophages in vitro.
Journal of Endocrinology (1996) 151, 113–118
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ABSTRACT
Rainbow trout were reared in black or off-white coloured tanks for up to 18 months of age to achieve maximum differences in the synthesis of the neuropeptide, melanin-concentrating hormone (MCH). White-reared fish had greatly increased MCH concentrations in their pituitary glands, in their MCH perikarya and in the presumptive neuromodulatory fibres of the dorsal hypothalamus/thalamus when compared with black-reared and commercially reared trout. Following transfer to brighter white tanks, white-reared fish showed a significant increase in plasma MCH concentration and a reduction of MCH in the pituitary and MCH perikarya. The additional challenge of repeated stress further increased plasma MCH concentration in these fish and also reduced MCH in the dorsal hypothalamus/thalamus. In black-reared fish transferred to white tanks, plasma MCH concentrations were significantly raised after transfer, although they were lower after 11 days than in white-reared counterparts. Transfer from black to white background caused a fall in the MCH concentration in all regions— pituitary gland, perikarya and dorsal hypothalamus/thalamus; if transfer was accompanied by repeated stress, the hormone in the pituitary gland and MCH perikarya became so depleted that plasma MCH concentrations declined. Within each experimental situation (control, background transfer and transfer with stress) there was in inverse correlation between plasma MCH concentrations of black- and white-reared fish and the cortisol concentration. MCH had no direct effect on the secretion of cortisol by interrenal tissue but incubated hypothalami, in which endogenous MCH had been immunoabsorbed, provided evidence that MCH can depress the release of corticotrophin-releasing bioactivity.
Journal of Endocrinology (1991) 128, 267–274
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Search for other papers by S. Moriyama in
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Search for other papers by T. Hirano in
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ABSTRACT
Our previous studies have shown that mammalian and salmon insulins stimulate sulphate uptake by cultured eel cartilage, suggesting the possible involvement of insulin in the regulation of cartilage matrix synthesis. In the present study, homologous eel insulin was isolated and characterized, and its effects on cartilage matrix synthesis and DNA synthesis were examined in vitro. Insulin was extracted from eel pancreas with acid–ethanol, and subsequently purified by isoelectric precipitation at pH 5·3, gel filtration on Sephadex G-50, and reversed-phase high-performance liquid chromatography. The amino acid composition and complete sequence (50 residues) of eel insulin revealed high homology to teleostean and mammalian insulins. The isolated eel insulin produced a more pronounced and longer lasting hypoglycaemic effect than bovine insulin in the eel. Homologous eel insulin, like bovine insulin-like growth factor (IGF-I) and insulin, stimulated sulphate uptake by cultured eel cartilage in a dose-dependent manner (16–1000 ng/ml). Combination experiments using maximal concentrations of bovine IGF-I (250 ng/ml) and increasing amounts of eel insulin (10–250 ng/ml) showed no additive effects of insulin on sulphate uptake, suggesting that insulin and IGF-I may share a common mechanism(s) of action. Eel insulin and bovine IGF-I also enhanced thymidine incorporation by eel cartilage in a dose-dependent manner (4–1000 ng/ml); eel insulin was equipotent with bovine IGF-I. These results suggest that insulin, like IGF-I, may exert direct growth-promoting actions in branchial cartilage of the eel.
Journal of Endocrinology (1992) 133, 221–230
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Search for other papers by H. Kawauchi in
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ABSTRACT
Somatolactin (SL), a newly discovered fish pituitary protein belonging to the GH/prolactin family, was isolated from coho salmon (Oncorhynchus kisutch). Antibodies were raised to purified coho SL, and a homologous radioimmunoassay was developed and validated. The assay was specific for SL as indicated by the absence of cross-reactivity with coho salmon GH, gonadotrophins I and II and less than 0·2% cross-reaction to prolactin. Serial dilutions of plasma and pituitary extracts from Oncorhynchus species including coho salmon, chinook salmon and rainbow trout were parallel to the coho salmon SL standard curve. Displacement curves for dilutions of Atlantic salmon (Salmo salar) plasma, but not pituitary extract were parallel to the standards. Plasma levels of SL were measured in coho salmon throughout the final year of reproductive maturation. During the period of gonadal growth, plasma SL levels increased and were highly correlated to oestradiol levels in females and 11-ketotestosterone levels in males. Peak levels of SL were observed at the time of final maturation and spawning in both sexes. It is hypothesized that SL may regulate some physiological aspect of reproduction.
Journal of Endocrinology (1992) 133, 393–403
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Search for other papers by H. Kawauchi in
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ABSTRACT
The seawater-adapting actions of GH, which are independent of growth, were studied in juvenile rainbow trout (Salmo gairdneri). Hormones examined were chum salmon (Oncorhynchus keta) GH (sGH) and prolactin (sPRL), and ovine GH (oGH). Plasma Na levels of freshwater-adapted fish peaked 24 h after transfer to 67% seawater and remained high for at least 48 h. Twenty-four hours after transfer, plasma Na levels were inversely correlated to body weight. In order to limit size and growth effects in all subsequent experiments, fish having a narrow range of body weights, fed a fixed diet, and injected with hormones over a short time-period were used. Plasma Na levels 24 h after transfer to 80% seawater were reduced significantly by sGH (0·25 and 2·5 μg/g) and oGH (2·5 μg/g) compared with saline injections, whereas sPRL (2·5 μg/g) had no significant effect. All the GH-treated fish had lower plasma Mg levels than controls; Ca levels were significantly reduced by the high dose of sGH. Salmon prolactin had no effect on concentrations of divalent ions. When the effects of a range of doses (0·01–1·25 μg/g) of sGH on plasma ion levels was tested, 0·25 μg/g was the most potent in reducing Na and Mg levels, while 1·25 μg/g alone reduced plasma Ca concentrations significantly. These studies show that the seawater-adapting actions of GH in trout are specific to that hormone and are not consequent to an increase in size.
J. Endocr. (1987) 112, 63–68
