Circannual Changes in Corticosterone Plasma Levels and Binding of Corticosterone to Plasma in Bufo japonicus formosus(Endocrinology)

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Corticosterone plasma levels were determined by radioimmunoassay in Bufo japonicus formosus captured each month in their natural environment. The maximal plasma level was recorded during the spring breeding season when life is purely aquatic, and the lowest in late summer. At the beginning of the active period, i. e. October or November, a slight increase occurred. The percentages of corticosterone bound to plasma proteins (total and specific binding) were evaluated simultaneously by a new micro-dialysis method. Since these percentages did not vary during the year, the circannual changes in corticosterone plasma levels (bound and free corticosterone) reproduced the circannual changes in free corticosterone plasma levels (active hormonal fraction). A relationship could be established between the highest corticosterone plasma levels and the intense locomotor activity associated to reproduction in spring. Corticosterone could act as a glucocorticoid, since its plasma level was higher when toads were fasting from the beginning of hibernation until summer. However, it was assumed that corticosterone could be also considered as a mineralocorticoid, the highest levels being observed during the only period of aquatic life in spring.
社団法人日本動物学会の論文