CHANGES IN THE HORMONE CONTENT OF THE HYPOTHALAMO-HYPOPHYSIAL SYSTEM OF THE RAINBOW TROUT (SALMO GAIRDNERI)

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Abstract
SUMMARY Fresh-water rainbow trout (Salmo gairdneri) subjected to handling showed an increase in pituitary and hypothalamic neurosecretory material. Transfer of fresh-water fish to sea water was accompanied by a significant decline in pituitary antidiuretic material (P < 0·01), possibly vasotocin, during the first 3 hr. There was a subsequent restoration to normal levels during the next 3 hr. The amount of oxytocic activity simultaneously increased and then returned to the control (fresh-water) level. Hypothalamic oxytocic content did not change significantly during the period immediately after transfer to sea water. It is possible, however, that the hypothalamic levels of a chromatographically distinct oxytocic substance ('substance P': Lederis, 1961) increased during the first few hours after transfer to sea water.