Influence of Seawater Adaptation on Prolactin and Growth Hormone Release from Organ-Cultured Pituitary of Rainbow Trout(Endocrinology)

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When immature rainbow trout (Oncorhynchus mykiss) were accliomated to 80% seawater for 2 weeks, the plasma osmolality and sodium level were slighlty but significantly higher than the levels in freshwater fish. Plasma prolactin (PRL) level of seawater-adapted fish was significantly lower than that of freshwater fish, whereas plasma growth hormone (GH) was significantly higher in seawater fish. Pituitary PRL and GH contents were significantly lower in seawater fish than in freshwater fish. When pituitaries were cultured in serum-free medium for 48 hr, an acute decrease in PRL release was seen within 12 hr in culture. Thereafter, a basal level of PRL release (0.2-0.5 ng/ pituitary-hr) was maintained, and the level was significantly lower in seawater fish than freshwater fish. On the other hand, GH release from the pituitary of both seawater and freshwater fish (200-500 ng/ pituitary-hr) was about 100 times greater than the basal PRL release throughtout the experiment, and there was no difference between the fish in seawater and those in fresh water. GH release from the trout pituitary seems to be predominantly under inhibitory control of the hypothalamus, thus resulting in an increased GH release under culture condition, and possibly masking the effect of seawater adaptation. The decreased PRL release in seawater-adapted fish may be related to the reduction in pituitary PRL content.
社団法人日本動物学会の論文
1991-10-15